LASIK with wavefront-guided and femtosecond technology superior
With wavefront-guided LASIK, the goal is to reduce all higher order aberrations
Preliminary results from a new study show that wavefront-guided ablations provide the best results for the vast majority of patients with the lowest rate of retreatment over conventional LASIK and wavefront optimized LASIK.
Reducing aberrations
Conventional LASIK induces higher order aberrations, including spherical aberration and coma, which are the most prominent. With optimized LASIK, the goal is not to change the spherical aberration target. The treatment basis is sphere and cylinder. Optimized simply means “not intended to induce spherical aberration,” and therefore does not address the patient’s spherical aberration or any other higher order aberrations. However, very few patients have zero spherical aberrations; those that do, are in their early 20s or younger. Numerous studies have shown that by the time most patients reach their 40s, they have positive spherical aberrations. With wavefront-guided LASIK, the goal is to reduce all higher order aberrations. The spherical aberration target is zero.
Study and results
The purpose of our study is to compare wavefront-optimized and wavefront-guided procedures to determine which is more effective. The retrospective chart review study of 200 IntraLASIK procedures included 100+ IntraLase (AMO) Wavelight (optimized) eyes and 100+ IntraLase VISX CustomVue (wavefront-guided) eyes. Pre-op and post-op wavefront scans were done on all eyes at a 6-mm pupil size Primary spherical aberrations, primary trefoil, and high order aberrations were measured. Thirty-nine CustomVue and 35 Wavelights were reviewed to this date (Figures 1 and 2).
These preliminary study results show that wavefront-guided ablation with femtosecond technology is optimal for the majority of patients who do not have zero spherical aberrations.
Overall, the wavefront-guided treatment induced significantly less higher order aberrations than the optimized procedure. There was significantly more variation with the optimized eyes. For best spectacle corrected low contrast letter acuity (BSCVA) at 5%, more wavefront-guided ablation patients achieved 20/20 than the optimized patients. When we looked at the contrast threshold using a 20/100 letter size for both groups, more wavefront-guided patients could read the lower contrast letters compared to the optimized group. This demonstrated that wavefront-guided ablation patients had better contrast letter acuity and lower contrast threshold.
For the study, the pre-op mean higher order aberration is 0.36 microns over a 6-mm pupil for both groups. With wavefront-guided, about 33% of patients were better, 33% were the same, and 33% were worse post-op. With wavefront–optimized, about 15% were better, 25% were the same, and 60% were worse. This shows that not trying to induce spherical aberrations doesn’t help 60% of the patients. The wavefront-guided ablations provide the best results for the majority of patients because they do not have zero spherical aberrations.
We are now evaluating the data on more than 100 eyes and we look forward to presenting the additional results from this study as they become available.
Wednesday, February 27, 2008
The changing face of refractive Lasik surgery
The changing face of refractive Lasik surgery
Several promising techniques are already availableAmetropia, when the eye needs corrective lenses to bring an image into focus, is common and has been so for centuries. The Roman emperor Nero observed gladiator fights through an emerald to correct his ametropia. The presence of 1 dioptre (D) of refractive error reduces Snellen visual acuity to less than 6/12
that is, below the level needed to drive. More than half of all eyes have a refractive error of greater than 1D and 15% have an error greater than 2D. Although the vast majority of patients will continue to wear spectacles or contact lenses, the popularity of refractive surgery to correct ametropia continues to grow. So too does the variety of surgical techniques available to correct ametropia. The factors exerting the greatest influence on refractive power are corneal curvature, the power of the lens, and axial length. The surgeon can thus act on the cornea or the natural lens with or without introducing artificial lenses. Assessing the best procedure for a particular refractive error is difficult because of the speed of change within this field. Most data come only from case series, and individual surgeons may also be limited by lack of experience in particular refractive techniques or by not having access to required equipment.
Myopia has been corrected for many years by radial keratotomy (radial corneal incisions), though this has few proponents in Britain. The advent of the excimer laser, with its ability to ablate tissue to submicron accuracy, has largely superceded radial keratotomy. The excimer laser can be used either on the surface, after removing corneal epithelium before treatment (photorefractive keratectomy), or within the stroma, after cutting a corneal flap (laser in situ keratomileusis or LASIK). In the United States over 70% of procedures performed are laser in situ keratomileusis, whereas in Britain most procedures are still photorefractive keratectomy.
The popularity of laser in situ keratomileusis is due to its "wow effect": visual recovery is almost instantaneous and painless. Patients are thrilled. After photorefractive keratectomy there may be considerable pain (unless a bandage contact lens is used), and the final result is not achieved for several months. However, the long term results of laser in situ keratomileusis in randomised trials seem to be no different from those of photorefractive keratectomy.There is a significant difference in price between the two procedures (twofold in some centres), with laser in situ keratomileusis also requiring considerably more training.
Myopia up to -5D is amenable to photorefractive keratectomy, and myopia of over -7D is best treated by laser in situ keratomileusis, with both procedures being acceptable between -5 and -7D. Worry about late ectasia (bulging of the cornea) is growing, and the maximum myopia treated with laser in situ keratomileusis is reducing (to maximum of -12D). There is considerable overlap between the degree of myopia treated by these two procedures based on surgeons' and patients' preference and cost. Case series suggest that complications with photorefractive keratectomy increase with the size of refraction and hence magnitude of treatment (haze and regression), whereas case series and a review of the literature on laser in situ keratomileusis show a 3-5% complication rate (flap related complications) regardless of treatment size. Vision of 6/12 or better is achieved in 94.4% of eyes with photorefractive keratectomy and in 49.2-83.2% of eyes with laser in situ keratomileusis. The degree of preoperative myopia is different in the two groups, however, so the difference in results reflects the higher degrees of error generally treated with laser in situ keratomileusis. The predictability reduces with increasing magnitude of correction and with additional treatment of astigmatism.
Other treatments for myopia are intracorneal rings and phakic intraocular lenses. The excitement about intracorneal rings for low to moderate myopia has waned as the surgery is difficult and also has a high risk of induced astigmatism, though initial results were comparable to those of other modes of surgery. Their main advantage is their reversibility. Phakic intraocular lenses (intraocular lenses inserted in the presence of the natural lens) start as low as -5D but are generally above -15D up to -30D (they are also available for long sightedness or hyperopia up to +10D). The advent of these lenses is very exciting for people with high myopia. Results from large series are scarce. There is also concern about the lens's effect on the natural lens or the cornea, depending on the type used. All intraocular surgery can end with an intraocular infectionwhich can be devastating; case series after other forms of intraocular surgery show infection rates of up to 0.3%.
Extreme myopia is probably best treated by a combination of phakic introcular lenses and laser in situ keratomileusis. Otherwise compromises are necessary because of the thickness of the lens and small optical zone. The alternative is to remove the natural lens and implant an artificial lens as in cataract surgery (also suitable for high hyperopia). This does, however, lead to loss of accommodation and is best suited for patients who need reading glasses; one case series showed that 42.3% of patients achieved vision of 6/12 unaided. Another series showed that this procedure is also suitable for patients with high hyperopia.
Hyperopia can be treated to +4D with photorefractive keratectomy and to +6D with laser in situ keratomileusis. The problem with hyperopia is that a wide treatment zone seems necessary for stability of treatment. However, the treatments do not seem to be as effective or as accurate as myopic corrections except in low corrections.
The future is difficult to predict. Solid state lasers will reduce the cost of equipment and improve the stability of laser energy output. Corneal inlay lenses and intrastromal picosecond lasers are under trial. Presbyopic treatments such as scleral implants seem unstable or variably effective at present but demand remains high. Even without these new developments, however, the ability to reduce refractive errors with reasonable accuracy is already here.
considering laser eye surgery should be warned of risks
People considering laser eye surgery should be warned of risks, says NICE
Laser surgery for short and long sightedness and astigmatism is generally safe and effective, but surgeons should make people aware of the potential risks compared with those of wearing glasses or contact lenses, guidance published last week says.
The guidance, for the NHS in England, Wales, and Scotland, found that the three most common types of laser eye surgery used to treat refractive errors—laser in situ keratomileusis (LASIK), photorefractive keratotectomy (PRK), and laser epithelial keratomileusis (LASEK)—shared similarly high effectiveness in improving visual acuity.
A systematic review of published evidence, commissioned by the National Institute for Health and Clinical Excellence (NICE) to develop the guidance, found that 91% of eyes treated for myopia or astigmatism with LASIK achieved within 1.0 dioptre of the intended correction at 3-12 months, compared with a median of 89% with PRK for myopia and 92% with LASEK for myopia and astigmatism.
A few patients had problems with laser eye surgery, however, including deterioration in visual acuity, development of new visual disturbances, and corneal infection. A median of 0.5% (range 0-20.5%) of eyes treated with PRK, 0% (0-8.2%) of eyes treated with LASEK, and 0.6% (0-3%) of eyes treated with LASIK lost visual acuity (measured as the loss of the ability to read two lines on an eye test chart with best glasses corrected vision). This was more likely to occur in people with severe shortsightedness.
Ectasia, a condition that can result from corneal thinning and that can lead to loss of vision, was seen in a median of 0.2% (0-0.87%) of eyes treated with LASIK, but rates were not reported after PRK or LASEK. The guidance noted, however, that many affected people might have been selected inappropriately for LASIK treatment. The guidance recommended that these risks should be weighed against those of wearing glasses or contact lenses.
Bruce Campbell, the chairman of the advisory committee that developed the guidance, said, “We hope the guidance will help to reassure people thinking of having laser eye surgery either on the NHS or privately. It is still important that patients discuss fully with the surgeon the possible risks and benefits of having laser surgery in their particular case. They need to weigh the risks of the procedure carefully against the inconvenience and possible risks of wearing spectacles or contact lenses.”
Professor Campbell added, “We are not saying that laser eye surgery should be offered to patients routinely on the NHS, because most people’s eye problems can easily be corrected by wearing spectacles or contact lenses.”
The guidance recommended that clinicians should audit and review clinical outcomes of all patients who have laser eye surgery, ideally including data from longer term follow-up. It also advised that clinicians should have adequate training before performing these procedures. Unlike other NICE guidance, guidance on interventions looks at the safety of procedures and at how well they work but does not make recommendations to the NHS about whether or not they should fund them.
PRK: The Original Laser Eye Surgery
PRK: The Original Laser Eye Surgery
It may be hard to believe these days, when everything is "LASIK this" and "LASIK that," but PRK (photorefractive keratectomy) used to be the most common refractive surgery procedure.
Both are grouped under the umbrella "laser eye surgery," but each is a little different when it comes to advantages and disadvantages.
LASIK patients have less discomfort and obtain good vision more quickly (with PRK improvement is gradual and over a few days or even months), but many surgeons prefer PRK for patients with larger pupils or thin corneas.
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PRK was invented in the early 1980s. The first FDA approval of a laser for PRK was in 1995, but the procedure was practiced in other countries for years. In fact, many Americans had the surgery done in Canada before it was available in the United States.
PRK is performed with an excimer laser, which uses a cool ultraviolet light beam to precisely remove ("ablate") very tiny bits of tissue from the surface of the cornea in order to reshape it. When you reshape the cornea in the right way, it works better to focus light into the eye and onto the retina, providing clearer vision than before.
Both nearsighted and farsighted people can benefit from PRK. With nearsighted people, the goal is to flatten the too-steep cornea; with farsighted people, a steeper cornea is desired. Also, excimer lasers can correct astigmatism, by smoothing an irregular cornea into a more normal shape.
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Before Surgery
If you are considering PRK, your first step is to choose a surgeon. [Read our article on how to choose a surgeon for advice on this subject.]
Your doctor will examine your eyes to determine exactly what kind of vision correction you need and how much laser ablation is needed. A corneal topographer will be used; this is an instrument that photographs your eye and creates a kind of "map" of your cornea. No one has a perfectly rounded cornea, and the topographer will display the corneal irregularities and the actual steepness or flatness that the surgeon must address.
Also your eye doctor will ask about other medical conditions you have. Some conditions may disqualify you altogether as a PRK candidate; others may mean a postponement of the procedure or special care afterward. [For more information on disqualifiers for LASIK and PRK, please read LASIK Criteria for Success.]
During Surgery
PRK is an ambulatory procedure; you walk into the surgery center, have PRK, and walk out again. In fact, the actual surgery usually takes less than a minute, and you're awake the whole time. Occasionally, the doctor will give a mild oral sedative beforehand.
Most people don't feel pain during PRK. Your eyes are first anesthetized with special drops. The doctor will have you lie down, then make sure your eye is positioned directly under the laser. (One eye is operated on at a time.) A kind of retainer is placed over your eye to keep your eyelids open — normally, this is not uncomfortable. It has a suction ring that keeps your eye pressurized and immobile.
The doctor uses a computer to adjust the laser for your particular prescription. You will be asked to look at a target light for a short time while he or she watches your eye through a microscope to make sure it remains in the correct position while the laser sends pulses of light to your cornea that painlessly remove the tissue. It's important to keep your gaze fixated on that target light in order to get the best results.
The laser machine will make a steady clicking sound while the laser pulses are happening, and you may smell a faintly acrid odor during the tissue removal. Don't worry, that's normal.
The higher your prescription, the more time the surgery will take.
The doctor may prescribe medication for any postoperative pain, but many people feel no more than mild discomfort or "scratchiness" afterward.
The surgeon has full control of the laser and can turn it off at any time. After the procedure is finished, you will rest for a little while. If you're having both eyes done the same day, the surgeon will probably do the other eye after a short period of time. Many people choose to have their second eye done a week later.
| Basics of vision correction surgery How to choose a LASIK surgeon How LASIK works Cost of LASIK What is LASEK? Presbyopia surgery |
After PRK
As with any kind of eye surgery, it's important that you follow your doctor's instructions to the letter. Get proper rest, fill and use any necessary prescriptions, and call your doctor immediately if you suspect a problem. What occurs after the surgery can affect your vision just as much as the surgery itself.
Immediately after PRK, the doctor will have you rest for a bit, then you can go home (someone else must drive). At home, you should relax for at least a few hours.
You may be able to go to work the next day, but many doctors advise a couple of days of rest instead. They also recommend no strenuous exercise for up to a week, since this can traumatize the eye and affect healing.
Avoid rubbing your eye (your doctor will tell you how long). In fact, you will be examined just about every day to make sure the epithelium is healing properly. You will probably wear a special "bandage" contact lens, use antibiotic drops for a few days, and apply anti-inflammatory drops for several weeks.
Most people achieve 20/20 or better vision with PRK (also true of LASIK). Some may achieve only 20/40 or not quite as good. In fact, 20/40 is fairly good vision. In most states, it is good enough for driving. Some patients may still need glasses or contact lenses following laser vision correction, though their prescription level will be much lower than before. [Read about outcome statistics elsewhere in this section.]
Postoperative complications can include infection and/or night glare (starbursts or halos that are most noticeable when you're viewing lights at night, such as while you're driving).
Even if you see perfectly after laser eye surgery, you may still need reading glasses or bifocal contact lenses once you hit your 40s. This is because the eye's lens stiffens as you age, a condition called presbyopia. Your distance vision will probably remain crisp, but seeing up close will be more difficult. However, researchers are studying ways to correct presbyopia surgically. So it's possible that you could have one of those procedures later, once they are FDA-approved. [Read more about surgical correction of presbyopia.]
All of these are important topics to discuss with your surgeon before deciding on the surgery
PRK: The Original Laser Eye Surgery
PRK: The Original Laser Eye Surgery
It may be hard to believe these days, when everything is "LASIK this" and "LASIK that," but PRK (photorefractive keratectomy) used to be the most common refractive surgery procedure.
Both are grouped under the umbrella "laser eye surgery," but each is a little different when it comes to advantages and disadvantages.
LASIK patients have less discomfort and obtain good vision more quickly (with PRK improvement is gradual and over a few days or even months), but many surgeons prefer PRK for patients with larger pupils or thin corneas.
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PRK was invented in the early 1980s. The first FDA approval of a laser for PRK was in 1995, but the procedure was practiced in other countries for years. In fact, many Americans had the surgery done in Canada before it was available in the United States.
PRK is performed with an excimer laser, which uses a cool ultraviolet light beam to precisely remove ("ablate") very tiny bits of tissue from the surface of the cornea in order to reshape it. When you reshape the cornea in the right way, it works better to focus light into the eye and onto the retina, providing clearer vision than before.
Both nearsighted and farsighted people can benefit from PRK. With nearsighted people, the goal is to flatten the too-steep cornea; with farsighted people, a steeper cornea is desired. Also, excimer lasers can correct astigmatism, by smoothing an irregular cornea into a more normal shape.
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Before Surgery
If you are considering PRK, your first step is to choose a surgeon. [Read our article on how to choose a surgeon for advice on this subject.]
Your doctor will examine your eyes to determine exactly what kind of vision correction you need and how much laser ablation is needed. A corneal topographer will be used; this is an instrument that photographs your eye and creates a kind of "map" of your cornea. No one has a perfectly rounded cornea, and the topographer will display the corneal irregularities and the actual steepness or flatness that the surgeon must address.
Also your eye doctor will ask about other medical conditions you have. Some conditions may disqualify you altogether as a PRK candidate; others may mean a postponement of the procedure or special care afterward. [For more information on disqualifiers for LASIK and PRK, please read LASIK Criteria for Success.]
During Surgery
PRK is an ambulatory procedure; you walk into the surgery center, have PRK, and walk out again. In fact, the actual surgery usually takes less than a minute, and you're awake the whole time. Occasionally, the doctor will give a mild oral sedative beforehand.
Most people don't feel pain during PRK. Your eyes are first anesthetized with special drops. The doctor will have you lie down, then make sure your eye is positioned directly under the laser. (One eye is operated on at a time.) A kind of retainer is placed over your eye to keep your eyelids open — normally, this is not uncomfortable. It has a suction ring that keeps your eye pressurized and immobile.
The doctor uses a computer to adjust the laser for your particular prescription. You will be asked to look at a target light for a short time while he or she watches your eye through a microscope to make sure it remains in the correct position while the laser sends pulses of light to your cornea that painlessly remove the tissue. It's important to keep your gaze fixated on that target light in order to get the best results.
The laser machine will make a steady clicking sound while the laser pulses are happening, and you may smell a faintly acrid odor during the tissue removal. Don't worry, that's normal.
The higher your prescription, the more time the surgery will take.
The doctor may prescribe medication for any postoperative pain, but many people feel no more than mild discomfort or "scratchiness" afterward.
The surgeon has full control of the laser and can turn it off at any time. After the procedure is finished, you will rest for a little while. If you're having both eyes done the same day, the surgeon will probably do the other eye after a short period of time. Many people choose to have their second eye done a week later.
| Basics of vision correction surgery How to choose a LASIK surgeon How LASIK works Cost of LASIK What is LASEK? Presbyopia surgery |
After PRK
As with any kind of eye surgery, it's important that you follow your doctor's instructions to the letter. Get proper rest, fill and use any necessary prescriptions, and call your doctor immediately if you suspect a problem. What occurs after the surgery can affect your vision just as much as the surgery itself.
Immediately after PRK, the doctor will have you rest for a bit, then you can go home (someone else must drive). At home, you should relax for at least a few hours.
You may be able to go to work the next day, but many doctors advise a couple of days of rest instead. They also recommend no strenuous exercise for up to a week, since this can traumatize the eye and affect healing.
Avoid rubbing your eye (your doctor will tell you how long). In fact, you will be examined just about every day to make sure the epithelium is healing properly. You will probably wear a special "bandage" contact lens, use antibiotic drops for a few days, and apply anti-inflammatory drops for several weeks.
Most people achieve 20/20 or better vision with PRK (also true of LASIK). Some may achieve only 20/40 or not quite as good. In fact, 20/40 is fairly good vision. In most states, it is good enough for driving. Some patients may still need glasses or contact lenses following laser vision correction, though their prescription level will be much lower than before. [Read about outcome statistics elsewhere in this section.]
Postoperative complications can include infection and/or night glare (starbursts or halos that are most noticeable when you're viewing lights at night, such as while you're driving).
Even if you see perfectly after laser eye surgery, you may still need reading glasses or bifocal contact lenses once you hit your 40s. This is because the eye's lens stiffens as you age, a condition called presbyopia. Your distance vision will probably remain crisp, but seeing up close will be more difficult. However, researchers are studying ways to correct presbyopia surgically. So it's possible that you could have one of those procedures later, once they are FDA-approved. [Read more about surgical correction of presbyopia.]
All of these are important topics to discuss with your surgeon before deciding on the surgery
Monovision Lasik
Monovision Lasik
Technique to reduce the need for reading glasses or bifocals with contacts, Lasik, and Lasik alternatives.
| Reading glasses become necessary in middle age. Although there is no "cure" for the underlying cause, monovision may be an appropriate workaround. |
Monovision is a technique to reduce the need for reading glasses or bifocals by working around presbyopia. Monovision can be accomplished with Lasik or contact lenses.
The need for near vision lenses is almost universal for people as they enter their middle years. As we mature, the natural crystalline lenses in our eyes become firm, enlarged, and will lose flexibility. This naturally occurring event will decrease the ability of the crystalline lens to vary its shape for different ranges of focus. This condition is known as presbyopia and is most often first detected in people between 40 and 50 years of age. A sure sign of presbyopia is when you cannot read without holding the item far away from you. For many, distance vision remains relatively unaffected by presbyopia.
Near Sight
When presbyopia occurs, most people do well with reading glasses, bifocals, or trifocal lenses. Reading glasses, bifocals, and trifocals are plus-powered lenses that would normally be used for someone who has hyperopia (farsighted, longsighted), however a plus-powered lens helps someone who is presbyopic because these lenses provide a small amount of myopic (nearsighted, shortsighted) vision.
There are two ways to describe myopia. One is that you cannot see things far away very well. The other is that you can see things close very well. People with a small amount of myopia can simply remove their glasses to read. However, people with previously normal vision, those already hyperopic, or those who wear contact lenses with full distance correction may need to use reading glasses for close work.
Even if not currently having problems with presbyopia, if contemplating refractive surgery and near age 40, after correction with refractive surgery a person may be hit with the immediate need for reading glasses due to a phenomenon we call "Sudden Presbyopia".
Bifocals and trifocals are used to provide both near and far vision without having to constantly put on and take off a pair of glasses or switch between two pairs of glasses.
Cannot Be Nearsighted and Farsighted
Because reading glasses provide a plus power that would normally be used to correct hyperopia, many people incorrectly believe they are becoming hyperopic. Those previously myopic may believe they are both hyperopic and myopic, which are mutually exclusive. Whenever changes in vision occur, it is always best to be evaluated by a competent eye care physician to determine the problem exactly.
Anyone who has needed to use readers, as they are often called, knows just how frustrating and irritating presbyopia can be. Many people have had excellent near and distant vision without glasses all their lives, until those dreaded readers become necessary because of presbyopia.
No Cure But A Reliable Workaround
There are currently no reliable and predictable surgery techniques or medications that will outright cure presbyopia, however there are a number of permanent and semi-permanent techniques to deal with the focusing changes and challenges caused by presbyopia. One of the more popular ways to work around presbyopia is with monovision correction. For many, monovision will reduce or eliminate the need for readers, bifocals, or trifocals. The concept of monovision is very simple. One eye is corrected for near vision and the other eye is corrected for distance vision. The brain figures out which eye to use and when. How to achieve monovision varies, depending upon the patient's current eyesight.
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If a person has never needed corrective lenses like glasses or contacts before, then a small amount of myopia can be induced in that person's non-dominant eye. The dominant eye remains uncorrected, as it already provides full distance vision. Download the USAEyes Dominant Eye Test and check which eye is dominant now.
If a person already has less than two diopters of myopia, that person's dominant eye can be fully corrected for distance vision, and the non-dominant eye not changed, which already provides good near vision.
People with greater amounts of myopia may have the dominant eye fully corrected to provide good distance vision, and the non-dominant eye undercorrected to less than two diopters myopic for good near vision. A patient who is already hyperopic may have the non-dominant eye overcorrected into myopia, plus the dominant eye either corrected for distance vision or untouched.
Contacts or Surgery
Monovision can be achieved through contact lenses or through refractive surgery. NearVision CK has been specifically approved by the FDA for monovision correction and is most ideal for patients who are mildly hyperopic or are plano and have never needed glasses. NearVision CK uses radio waves to change the shape of the cornea and create a small amount of myopia in the non-dominant eye. This myopia provides near vision, while the other uncorrected eye provides distance vision. NearVision CK is considered temporary because the effect does diminish with time, however the regression of the NearVision CK effect is very slow and can last for years.
Although not specifically approved by the FDA for monovision, the use of Lasik, LASEK, PRK, and Epi-Lasik are also appropriate techniques to create monovision as an off label use of the excimer laser.
The chief advantage of monovision is the freedom it can provide from reading glasses. After six to eight weeks the brain makes the vision changes automatically, without any conscious effort or awareness. Monovision makes it possible to repeatedly change the range of focus, without having to constantly remove or add corrective lenses.
Monovision Drawbacks
As with many good things, monovision comes with some disadvantages. People with monovision may have some degree of decreased depth perception unless corrective lenses are used to fully correct the slightly myopic eye. They may also notice blurred vision in the "near" eye when glancing in the side mirror of their cars or when the vision in the "distance" eye is blocked by an object.
We highly recommend someone with monovision have a pair of glasses made that provide full distance vision correction for those situations where excellent distance vision and/or depth perception are desirable. For detail activities such as prolonged reading, have a pair of reading glasses made that provide balanced near vision. It may be possible to purchase an identical pair of readers with two different powers of correction, and switch lenses to provide the balance to full near correction with both monovision eyes.
Try In Contacts First
If monovision seems desirable, you should try to achieve the effect with contact lenses prior to surgery to determine if monovision is suitable for your individual needs and your ability to adapt. Should you initially choose surgical monovision and subsequently become unhappy with it, enhancement surgery to fully correct the undercorrected eye and reverse the monovision effect is often an option.
People who are entering mid-life and are interested in monovision should discuss the matter with their doctor prior to undergoing surgery. It is surprising how many patients adapt readily and happily to this vision option, however monovision is not for everybody and some people dislike its effect.
Detailed Lasik Information
Lasik
Detailed Lasik Information, video, and comparison to alternatives.
 Lasik applies laser energy under a flap of corneal tissue to correct nearsighted vision, farsighted vision, and astigmatism. Click for video. |
Lasik is the most often performed surgery in the US. Conventional or wavefront custom Lasik is a surgical procedure that changes the shape of the cornea to reduce the need for glasses or contacts. Lasik has many distinct advantages over other refractive surgery procedures, but also has limitations that may indicate something else or no surgery is best for an individual patient.
The most you can expect from Lasik is the convenience of a reduced need for corrective lenses. To achieve that convenience, you must accept some risk. We hope to help you minimize that risk, but risk cannot be eliminated.
This document discusses in detail the history of Lasik, some of Lasik's advantages, and many of Lasik's disadvantages. This long and detailed article is to help a potential Lasik patient understand in depth what Lasik can do, might do, and when it is likely to do what is desired. Much of this discussion compares Lasik with other refractive surgery procedures, including PRK, LASEK, Epi-Lasik, P-IOLs, and RLE.
The primary difference between Lasik and other cornea based procedures is where the excimer laser ablates: under a flap of corneal tissue. Lasik is actually the combination of Photorefractive Keratectomy (PRK) and Automated Lamellar Keratoplasty (ALK). As you will see, the Lasik flap is both Lasik's strength, and its weakness.
As with nearly all excimer laser based refractive surgery, Lasik can be performed with both conventional ablation and wavefront-guided ablation.
ALK was refined over the ensuing decades, but complexity of the microkeratome, unpredictable results, and difficulty of the procedure kept its adoption out of the mainstream. The development and popularization of Radial Keratotomy (RK) in the 1980s provided a more reliable means to correct refractive error, although ALK still had its fans in ophthalmology and the technology behind ALK continued to advance.
PRK haze does not normally form for corrections that require a moderate amount of tissue removal, generally less than about 6.00 diopters of refractive error. That is good news for moderate and low myopia and virtually all hyperopes (farsighted, longsighted), but bad news for those needing higher corrections. As a general rule, if you need less than 6.00 diopters of correction, you should consider PRK as an option.
Refinements in technology and technique have reduced the severity and probability of complications, but even with continued refinement, no surgery is perfect and there will always be some who will have unexpected and undesired outcomes. The primary purpose of the our organization is to help prospective patients become informed of the issues that contribute to poor outcomes, avoid those problems, and find the best qualified doctor available.
If the flap exists, there will be the possibility of flap related problems. Those potential problems do not stop when you leave the surgery suite. Once you have had Lasik you have always had Lasik and you must always consider that your eye is fundamentally and forever changed. Change can be a good thing, but sometimes not.
There is a movement in ophthalmology back toward the surface ablation techniques of PRK and its cousins LASEK and Epi-Lasik because surface ablation eliminates the Lasik flap. If you eliminate the flap, you do not just reduce the possibility of a flap complication, you eliminate it completely. Everybody likes eliminating the possibility of a problem.
The advantage of surface ablation techniques go beyond just eliminating the possibility of flap complications. Study after study have shown that PRK produces long-term results that are equal to or superior than Lasik. A part of the reason for these better outcomes is the availability of enhanced ablation patterns with wavefront technology. Long term, PRK is often better for a patient than Lasik. The problem is, we don’t “see” long term.
The epithelium is the outermost layer of the cornea. These are the fastest reproducing cells in the human body. Before the laser can remove corneal tissue with PRK, all epithelial cells must be removed over the treatment area. The epithelial cells will regenerate and cover the treatment area in about 3-6 days. They will thicken over the ensuing 2 weeks, and smooth at about 6-8 weeks. Those time periods sound familiar? That’s right, all the slow vision recovery of PRK is directly related to the epithelium recovery. Also, comfort is related to epithelium recovery.
In LASEK, a diluted solution of alcohol is applied to the cornea for a few seconds. This disrupts the epithelial cell’s ability to hold on to Bowman’s layer, the next layer down the corneal construction. These disrupted, but viable, cells are moved out of the way, the laser does its magic, and then the cells are moved back over the treatment area. In theory, LASEK will hasten recovery, limit pain, and reduce the probability of haze. I’m sure you remember what we said about theories.
The reality is that few of the epithelial cells survive the alcohol. While the dead or dying cells replaced over the treatment area do provide extra protection and appear to reduce discomfort, vision recovery is not significantly improved. Improved, yes, but nothing like a Lasik recovery. While a reduction in corneal haze was noted, this may be attributed more to the advancement in laser quality than the LASEK procedure. Doctors are seeing less haze with PRK today, even thought PRK does not keep the epithelium. Detailed LASEK Information
The latest in the attempt to save the epithelium is Epi-Lasik. This technique uses a mechanical microkeratome with a blunt, rather than sharp, blade that slides across the front of the cornea. This blunt blade scrapes up a sheet of epithelium at the surface of the stronger Bowman’s layer. This is essentially an epithelial flap. The flap is moved out of the way similar to Lasik, the laser treats the exposed area, and then the epithelial flap is repositioned. Early reports indicate that there is improvement in recovery time, comfort, and even the probability of haze, but it is much too early to know if Epi-Lasik is really ready for prime time. Detailed Epi-Lasik Information
Using a wavefront-guided ablation is often called custom Lasik, custom PRK, CustomVue, CustomCornea, or Zyoptix, depending upon the laser used. The process uses a wavefront aberrometer to evaluate virtually all of the optics that affect your vision. From this wavefront derived information, an ablation profile is created with the intent of reducing the introduction of harmful aberrations to your optics, and reducing those that already exist.
Think of wavefront as a mapping system. If you wanted to travel from Cleveland to Beverly Hills, a map of the whole US showing all the major highways would do just fine. If you wanted to get to a specific street corner on Rodeo Drive, you would need the detail of a city map. Think of conventional laser ablation as a map of the US, and wavefront-guided ablation as a street map.
The wavefront ablation profile of where more tissue needs to be removed here and less tissue needs to be removed there is very nuanced with tiny changes across the treatment area. A problem with Lasik is that you are putting a relatively thick 100-180 micron flap of corneal tissue on top of this fancy nuanced ablation. Like too many blankets on the bed, you lose some of the detail of the shape of who is in that bed.
Yet another reason why there is a push toward PRK in some circles is that the lasers are now able to make these really nice detailed ablations, but some of that detail is muted by the Lasik flap. Also, the Bowman’s layer and uppermost layer of cells of he cornea are more dense than the deeper stromal layer. It is opined that this may help in creation of better and better ablations.
It has been found that having a patient take 500mg of vitamin C (yes, plain old vitamin C) twice a day for a week before PRK and at least two weeks after surgery significantly reduces the incidence of corneal haze. Isn’t it always the simple answer that is the best. This appears to be helpful, but more study is needed to determine just how much help is provided with oral vitamin C supplements. It is really not known if vitamin C is enough for someone who needs 8.00 diopters of correction, but is not enough for someone who needs 10.00. The limits need to be determined.
The use of the topical eye drop Mitomycin C dramatically reduces the probability of haze, and can be used to treat haze when it occurs, but this is rather strong medicine. Mitomycin C is appropriate when required, but probably needs to be avoided if possible. Also, Mitomycin C changes how much tissue the laser ablates with each pulse, so the doctor needs to manually change the treatment plan. This requires additional expertise.
As a gross generalization, Lasik is probably best for someone with more than 6.00 diopters of correction, and almost certainly necessary for someone needing more than 10.00 diopters of correction. Less than 6.00 diopters would make PRK, LASEK, and Epi-Lasik added possibilities. Between 6.00 diopters and 8.00 diopters, LASEK, Epi-Lasik, or PRK with Mitomycin C would be added to the mix. If you require fast recovery and can’t handle even a small amount of discomfort, then Lasik and possibly Epi-Lasik are the prime choices. Over 12.00 diopters of myopic correction and over about 3.00 diopters of hyperopic correction would indicate that cornea based surgery is probably not wise and alternatives such as P-IOLs or RLE should be considered. Although Lasik is approved for much higher corrections, that does not mean that very high refractive error should be corrected with Lasik in your case.
Remember, these are gross generalizations and upon examination your doctor may recommend something completely different. And of course, it may be that no refractive surgery of any kind is appropriate for you.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgery Doctor.
The most you can expect from Lasik is the convenience of a reduced need for corrective lenses. To achieve that convenience, you must accept some risk. We hope to help you minimize that risk, but risk cannot be eliminated.
This document discusses in detail the history of Lasik, some of Lasik's advantages, and many of Lasik's disadvantages. This long and detailed article is to help a potential Lasik patient understand in depth what Lasik can do, might do, and when it is likely to do what is desired. Much of this discussion compares Lasik with other refractive surgery procedures, including PRK, LASEK, Epi-Lasik, P-IOLs, and RLE.
The primary difference between Lasik and other cornea based procedures is where the excimer laser ablates: under a flap of corneal tissue. Lasik is actually the combination of Photorefractive Keratectomy (PRK) and Automated Lamellar Keratoplasty (ALK). As you will see, the Lasik flap is both Lasik's strength, and its weakness.
As with nearly all excimer laser based refractive surgery, Lasik can be performed with both conventional ablation and wavefront-guided ablation.
In The Beginning
ALK was developed in the 1950s as a method of refractive surgery. A mechanical microkeratome is affixed to the eye with a suction ring. A plate flattens the cornea and a very sharp metal blade passes through the top of the flattened cornea, creating a thin slice of tissue. In original ALK, additional shavings of the cornea were removed to cause a net flattening of the central cornea. Flattening the center of the cornea will cause a change in the way light bends through the cornea, correcting myopia (nearsighted, shortsighted). The more tissue that is removed, the more the center becomes flat, and more refractive correction occurs.ALK was refined over the ensuing decades, but complexity of the microkeratome, unpredictable results, and difficulty of the procedure kept its adoption out of the mainstream. The development and popularization of Radial Keratotomy (RK) in the 1980s provided a more reliable means to correct refractive error, although ALK still had its fans in ophthalmology and the technology behind ALK continued to advance.
The Laser Is Introduced
Lasers have been used successfully for eye care for decades. A laser is only highly condensed light and just about everything your eye doctor does deals with light. PRK was the first refractive treatment to use an excimer laser to remove tissue. An excimer laser changes the chemical nature of the molecules that hold together the cells of the cornea. The change causes this “glue” to release the corneal cells, and they rapidly escape from the cornea in a plume that looks very much like an atomic bomb blast, but is significantly different in its cause and effect. The excimer laser does not “burn” the cornea or cut the cornea. It makes the corneal fall apart, microscopic layer by microscopic layer. You cannot talk about Lasik without talking about PRK. Detailed PRK InformationThe Cornea Responds
A major problem with PRK in its early development was corneal haze. PRK related haze continues to be a problem to this day, although some techniques have been developed to control its severity and treat its occurrence. Corneal haze is caused by the cornea’s wound response. Surgery is an insult to the cornea, and your cornea really doesn’t care if you want this insult, it is going to respond as if it has been wounded. A part of that wound response causes opaque cells to form. This presents as white hazing of the cornea, restricting light from passing through, and reducing the quality of vision.PRK haze does not normally form for corrections that require a moderate amount of tissue removal, generally less than about 6.00 diopters of refractive error. That is good news for moderate and low myopia and virtually all hyperopes (farsighted, longsighted), but bad news for those needing higher corrections. As a general rule, if you need less than 6.00 diopters of correction, you should consider PRK as an option.
Different Depths, Different Responses
It was noted that wound response to laser ablation deeper in the cornea is significantly different than when the ablation is performed at the outer surface of the cornea. The idea was formed to creating a flap of corneal tissue using ALK methods, perform the PRK ablation under the flap and deeper in the cornea, then returning the flap over the ablated area. Thus Lasik was created as a combination of ALK and PRK.Fool’s Paradise
Lasik literally “fools” the cornea into not knowing it has been wounded. This is why Lasik normally provides no pain, has an almost instant vision recovery, and almost never causes corneal haze; the cornea doesn’t know it has had surgery. You could call this microsurgery’s own “ignorance is bliss”. This major advancement allows correction of very high refractive error without a high risk of corneal haze and subsequent loss of vision quality.More Than One Way To….
Due to new demand caused by the creation of Lasik, rapid advancement in mechanical microkeratome technology has provided much better quality corneal flaps with more predictability of size and thickness. Additionally, the femtosecond laser has been refined to create flaps with laser energy, rather than a metal blade. Intralase is the first company to introduce this technology to the US and Lasik with a laser created flap is often called All-Laser Lasik or “all laser Lasik”. Detailed Intralase All-Laser Lasik InformationNot All 20-Minute Miracles
The only way to describe the implementation and popularity of Lasik is as an explosion. Ophthalmologists were rushing to lean how to perform this new procedure that promised to give patients freedom from glasses with no pain and almost instant results. Patients were flocking to clinics looking for freedom from glasses and contacts. That was the theory of what would happen. There is nothing that can screw up a perfectly good theory faster than reality.Reality Sometimes Bites
While the vast majority of patients received a seemingly miraculous improvement in uncorrected vision, a small but very important minority had complications ranging from nuisance to vision debilitating. Much was learned by the early problems with Lasik. The range of refractive error treated today is significantly more narrow than in the early years. You will virtually never see a 20.00 diopter myope have Lasik today. This was not always the case.Refinements in technology and technique have reduced the severity and probability of complications, but even with continued refinement, no surgery is perfect and there will always be some who will have unexpected and undesired outcomes. The primary purpose of the our organization is to help prospective patients become informed of the issues that contribute to poor outcomes, avoid those problems, and find the best qualified doctor available.
Back To The Future
The basics of Lasik today are virtually the same as when first created: make a flap, zap the cornea, and replace the flap. The range of variables in this three-step process is ever increasing, as are the number of options. What we discuss here are some of the options available today – old and new – and their relative advantages/disadvantages. If you visit our article on Intralase, you will learn the details of the creation options of the corneal flap, but all flaps have potential problems, no matter how they are made. The first problem of the Lasik flap is the existence of the flap itself.If the flap exists, there will be the possibility of flap related problems. Those potential problems do not stop when you leave the surgery suite. Once you have had Lasik you have always had Lasik and you must always consider that your eye is fundamentally and forever changed. Change can be a good thing, but sometimes not.
There is a movement in ophthalmology back toward the surface ablation techniques of PRK and its cousins LASEK and Epi-Lasik because surface ablation eliminates the Lasik flap. If you eliminate the flap, you do not just reduce the possibility of a flap complication, you eliminate it completely. Everybody likes eliminating the possibility of a problem.
The advantage of surface ablation techniques go beyond just eliminating the possibility of flap complications. Study after study have shown that PRK produces long-term results that are equal to or superior than Lasik. A part of the reason for these better outcomes is the availability of enhanced ablation patterns with wavefront technology. Long term, PRK is often better for a patient than Lasik. The problem is, we don’t “see” long term.
Lasik and PRK Recovery
The recovery from PRK is vastly different than Lasik. With Lasik, it is probable that fully functional vision will be almost instantaneous, there will be almost no pain, and you can resume most normal activities almost immediately. PRK, on the other hand, provides “fuzzy functional” vision for 3-6 days, functional vision for about another 2 weeks, and you won’t get the really good crisp vision you desire for about 6-8 weeks after surgery. Not everyone can afford this much time with compromised vision. There is much more discomfort associated with PRK, and even today PRK has limitations due to haze, but let’s consider how the haze situation has improved.LASEK and Epi-Lasik
The ideal situation would be to have surface ablation with no pain, little probability of haze, and instant recovery. In other words, Lasik without the flap that reduces the probability of these limitations and speeds vision recovery. The answer to Lasik without the flap may be in changing the depth the flap.The epithelium is the outermost layer of the cornea. These are the fastest reproducing cells in the human body. Before the laser can remove corneal tissue with PRK, all epithelial cells must be removed over the treatment area. The epithelial cells will regenerate and cover the treatment area in about 3-6 days. They will thicken over the ensuing 2 weeks, and smooth at about 6-8 weeks. Those time periods sound familiar? That’s right, all the slow vision recovery of PRK is directly related to the epithelium recovery. Also, comfort is related to epithelium recovery.
Save The Epithelium!
Obviously, if the epithelium is so helpful, it needs to be saved. Lasik leaves the epithelium in place because the Lasik flap is cut deep underneath the epithelium in the deeper stromal layer of the cornea. Two similar but separate techniques to save the epithelium have been developed; LASEK and Epi-Lasik.In LASEK, a diluted solution of alcohol is applied to the cornea for a few seconds. This disrupts the epithelial cell’s ability to hold on to Bowman’s layer, the next layer down the corneal construction. These disrupted, but viable, cells are moved out of the way, the laser does its magic, and then the cells are moved back over the treatment area. In theory, LASEK will hasten recovery, limit pain, and reduce the probability of haze. I’m sure you remember what we said about theories.
The reality is that few of the epithelial cells survive the alcohol. While the dead or dying cells replaced over the treatment area do provide extra protection and appear to reduce discomfort, vision recovery is not significantly improved. Improved, yes, but nothing like a Lasik recovery. While a reduction in corneal haze was noted, this may be attributed more to the advancement in laser quality than the LASEK procedure. Doctors are seeing less haze with PRK today, even thought PRK does not keep the epithelium. Detailed LASEK Information
The latest in the attempt to save the epithelium is Epi-Lasik. This technique uses a mechanical microkeratome with a blunt, rather than sharp, blade that slides across the front of the cornea. This blunt blade scrapes up a sheet of epithelium at the surface of the stronger Bowman’s layer. This is essentially an epithelial flap. The flap is moved out of the way similar to Lasik, the laser treats the exposed area, and then the epithelial flap is repositioned. Early reports indicate that there is improvement in recovery time, comfort, and even the probability of haze, but it is much too early to know if Epi-Lasik is really ready for prime time. Detailed Epi-Lasik Information
Detailing the Details of Detailed Ablations
If you are considering Lasik, you are going to hear about wavefront. You are going to hear a lot about wavefront. You are going to be inundated with wavefront this and wavefront that. Click Wavefront Guided Ablation for a detailed article about whether or not you require a wavefront-guided ablation. In this article we will discuss how wavefront-guided ablation relates to Lasik.Using a wavefront-guided ablation is often called custom Lasik, custom PRK, CustomVue, CustomCornea, or Zyoptix, depending upon the laser used. The process uses a wavefront aberrometer to evaluate virtually all of the optics that affect your vision. From this wavefront derived information, an ablation profile is created with the intent of reducing the introduction of harmful aberrations to your optics, and reducing those that already exist.
Think of wavefront as a mapping system. If you wanted to travel from Cleveland to Beverly Hills, a map of the whole US showing all the major highways would do just fine. If you wanted to get to a specific street corner on Rodeo Drive, you would need the detail of a city map. Think of conventional laser ablation as a map of the US, and wavefront-guided ablation as a street map.
The wavefront ablation profile of where more tissue needs to be removed here and less tissue needs to be removed there is very nuanced with tiny changes across the treatment area. A problem with Lasik is that you are putting a relatively thick 100-180 micron flap of corneal tissue on top of this fancy nuanced ablation. Like too many blankets on the bed, you lose some of the detail of the shape of who is in that bed.
Yet another reason why there is a push toward PRK in some circles is that the lasers are now able to make these really nice detailed ablations, but some of that detail is muted by the Lasik flap. Also, the Bowman’s layer and uppermost layer of cells of he cornea are more dense than the deeper stromal layer. It is opined that this may help in creation of better and better ablations.
Why Not Abandon Lasik For surface ablation?
At first glance, it would seem that everyone should be jumping back on the PRK bandwagon. Not always. There is still that issue of corneal haze. The newer lasers seem to reduce the probability of corneal haze with PRK, but do not eliminate it. LASEK and Epi-Lasik attempt to minimize the limitations of PRK by saving the epithelium, but they may turn out to be just so much expensive luggage.It has been found that having a patient take 500mg of vitamin C (yes, plain old vitamin C) twice a day for a week before PRK and at least two weeks after surgery significantly reduces the incidence of corneal haze. Isn’t it always the simple answer that is the best. This appears to be helpful, but more study is needed to determine just how much help is provided with oral vitamin C supplements. It is really not known if vitamin C is enough for someone who needs 8.00 diopters of correction, but is not enough for someone who needs 10.00. The limits need to be determined.
The use of the topical eye drop Mitomycin C dramatically reduces the probability of haze, and can be used to treat haze when it occurs, but this is rather strong medicine. Mitomycin C is appropriate when required, but probably needs to be avoided if possible. Also, Mitomycin C changes how much tissue the laser ablates with each pulse, so the doctor needs to manually change the treatment plan. This requires additional expertise.
Lasik & Many Options
To get the best possible outcome, one must play the odds. You cannot guarantee perfection, but you and your doctor can take many steps to reduce the probability of a bad outcome. Procedure selection is one of those steps. It is not that Lasik is always best, or PRK should be used whenever possible, it is more that depending upon your unique circumstances, Lasik may or may not be the best choice for you. There is nothing wrong with Lasik as a procedure, if it is the best procedure for your situation.As a gross generalization, Lasik is probably best for someone with more than 6.00 diopters of correction, and almost certainly necessary for someone needing more than 10.00 diopters of correction. Less than 6.00 diopters would make PRK, LASEK, and Epi-Lasik added possibilities. Between 6.00 diopters and 8.00 diopters, LASEK, Epi-Lasik, or PRK with Mitomycin C would be added to the mix. If you require fast recovery and can’t handle even a small amount of discomfort, then Lasik and possibly Epi-Lasik are the prime choices. Over 12.00 diopters of myopic correction and over about 3.00 diopters of hyperopic correction would indicate that cornea based surgery is probably not wise and alternatives such as P-IOLs or RLE should be considered. Although Lasik is approved for much higher corrections, that does not mean that very high refractive error should be corrected with Lasik in your case.
Remember, these are gross generalizations and upon examination your doctor may recommend something completely different. And of course, it may be that no refractive surgery of any kind is appropriate for you.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgery Doctor.
Video courtesy University of Illinois Eye & Ear Infirmary.
Returning To Work After Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, CK, P-IOL, RLE, etc
Returning To Work After
Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, CK, P-IOL, RLE, etc.
When you can return to work after refractive surgery will depend on the type of refractive surgery, the amount of refractive error, what complications are present after surgery (if any), and the type of work you do. Refractive surgery often is more a six-month process than a 20-Minute Miracle Although many refractive surgery patients are back to work the next day, others have great difficulty for days and weeks.
It is reported that hat Lasik, All-Laser Lasik, CK, and Intacs provide clarity almost immediately after surgery while PRK, LASEK, and Epi-Lasik may take a few days to weeks.
It is not unusual for the immediate post-operative presence of complications such as ghosts, arcs, starbursts, halos, regular and irregular astigmatism, and other potential problems that can significantly reduce clarity from a short period of time to permanently. Usually these symptoms dissipate with healing over a period of weeks or months, however additional treatment may be necessary if such problems occur.
The IOL based P-IOL and RLE are significantly more invasive surgeries than Lasik, All-Laser Lasik, CK, Intacs, PRK, LASEK or Epi-Lasik and have a very different and longer recovery period.
Working at a computer seems to be problematic for some people after refractive surgery. The distance from the monitor and the nature of projected light seems to cause fatigue and even headaches. People tend to not blink as often when working long hours at a computer. Strenuous work or work that might cause injury to your eye should be avoided until the eye has healed enough to withstand the normal risk of trauma. It is very important that the eye is protected from being hit, poked, or rubbed. If you are an athlete, don't expect your doctor to okay you standing at bat with a baseball being thrown near your head at 70 miles per hour. If you are a gardener you will need to refrain from work or wear protective goggles for some time. Everyone's individual situation needs to be evaluated based upon the probability of contact with the eye. Because of possible fluctuation in your vision immediately post-operative you should avoid long periods that would require detailed use of your eyes.
Since every person is different and every situation is unique, it will be necessary to discuss with a competent doctor the probable recover period and when the patient can return to work.
What Was That Smell? During Lasik
What Was That Smell?
During Lasik
Some patients experience unpleasant order during Lasik, All-Laser Lasik, PRK, LASEK, or Epi-Lasik. It's not what you might think.
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After completing conventional or wavefront custom Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, laser eye surgery, patients often exclaim, "I can see!", shortly followed by, "What was that smell?" The process of laser eye surgery can cause the disconcerting smell of burning flesh.
The excimer laser is a "cold" laser and does not remove tissue with heat. The concentrated light frequency disrupts the molecular bonds that hold together the corneal cells. Without these bonds the cells escape in a the form of a mushroom cloud that looks similar to an atomic bomb.
As these cells rapidly move away from the cornea they strike each other causing a minor heat buildup from friction. That buildup can raise the temperature of the cornea to about 110°F (43°C), or around 11°F (6°C) above normal body temperature and very close to the water temperature of a nice warm hot tub. A second-degree burn threshold is skin temperature raised to 175°F (79°C). A third-degree burn threshold is skin temperature raised to 200°F (93°C).
The smell, which is remarkably like the smell of burning flesh, is from the chemical reaction of the laser on the cornea, not from heat.
Some surgeons use a special vacuum device surrounding the eye that removes these cells throughout the procedure so the source of the unpleasant smell is removed. Even if it is only a chemical reaction via laser and not heat, nobody wants to experience what smells like their eye burning.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgery Doctor.
Astigmatism Correction:Issues with Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, P-IOL, RLE, CK, etc.
Astigmatism Correction
Issues with Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, P-IOL, RLE, CK, etc.
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Conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, and CK can correct astigmatism. Most refractive surgeons consider it much more difficult to correct astigmatism than myopia (nearsighted, shortsighted) or hyperopia (farsighted, longsighted). As a very general rule, if your astigmatism is more than half your sphere, then the probably of a good outcome is diminished. If your astigmatism is more than 2.00 diopters, your probably of a good outcome is significantly diminished.
Lens Based Limitations
Lens based refractive surgery procedures like P-IOL and RLE do not correct astigmatism well, however RLE can correct lenticular astigmatism. Although toric intraocular lenses (IOL) are available, placement and rotation issues make astigmatic correction difficult.
The amount and type of astigmatism that can be corrected will depend upon many factors. Lasers are approved by the FDA for specific levels of astigmatic correction. We have a laser specification table that can show you exactly what degree of astigmatic correction - if any - a laser is approved to perform. More than the laser, the physiological features of your eye will determine if your astigmatism can be corrected with refractive surgery. Issues such as thickness of cornea, pupil size, plus type and amount of astigmatism will all be important considerations.
Indirectly Correct Astigmatism
CK, P-IOL, and RLE do not directly correct astigmatism, however a minor amount of astigmatism can be corrected as a part of the surgical process of correcting myopia or hyperopia. CK can position the spots of radiofrequency energy to correct a small amount of astigmatism. P-IOLs available in the US do not correct astigmatism, but the incision through which the P-IOL is placed inside the eye can be manipulated to reduce preexisting astigmatism. Equally, the incision created during RLE through which the IOL is placed inside the eye can be manipulated to reduce preexisting astigmatism.
Laser Coupling Effect
Something important to remember is that with most laser assisted astigmatic refractive surgery techniques, for each diopter of astigmatism that is corrected, a certain amount of myopia is also automatically corrected - even if you don't need the myopia correction. This coupling of myopic correction and astigmatic correction is consistent with virtually all excimer lasers.
As an example, let us assume that for every one diopter of astigmatic correction the technique also corrects 0.25 diopter of myopia. If you have 2.00 diopters of astigmatism, you will receive 0.50 diopters of myopia correction (0.25 diopters of automatic myopia correction multiplied by the 2.00 diopters of astigmatism to be corrected) even if you do not need the myopia correction. If you have more than 0.50 diopters of myopia, a 2.00 diopter astigmatic correction should not be a problem with this technique. If you are plano then after surgery you would be 0.50 diopters hyperopic - not a desirable outcome.
Different Astigmatism Types
Irregular astigmatism is very, very difficult to correct and some techniques and technology cannot fully correct an irregular astigmatism at this time. Every person with irregular astigmatism is unique and needs to be individually evaluated.
Lenticular astigmatism is when the irregularity is in the natural crystalline lens, rather than in the cornea. RLE will eliminate lenticular astigmatism. Cornea-based surgery techniques conventional and wavefront Lasik, All-Laser Lasik, PRK, LASEK, and Epi-Lasik can correct lenticular astigmatism's effects, but making a reverse of the lenticular astigmatism in the cornea. While this can be a successful technique of lenticular astigmatism correction, there is a significant concern.
As we age the natural lens of the eye becomes clouded. This is called a cataract. The process to resolve a cataract is to remove the natural lens and replace it with an artificial lens. The problem is that the artificial lens will not have the pre-existing lenticular astigmatism and if the cornea has been reshaped to accommodate the lenticular astigmatism, the cornea will now cause an irregular astigmatism.
Discuss in detail with your doctor the type and amount of astigmatism you have and how it may be accommodated with refractive surgery. Discuss if the technology and techniques s/he intends to use may affect myopic correction and how this may be accommodated for your individual needs.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgeon.
Corneal Abrasion:Abrasions of the cornea are problematic with Lasik, All-Laser Lasik, Epi-Lasik, CK, RLE, and P-IOL.
Corneal Abrasion
Abrasions of the cornea are problematic with Lasik, All-Laser Lasik, Epi-Lasik, CK, RLE, and P-IOL.
A corneal abrasion is a scratch on the cornea. When there is trauma to the cornea, such as with a finger or object, the epithelium, Bowman's layer, and stroma of the cornea can be scratched, resulting in a corneal abrasion. A patient with a corneal abrasion undoubtedly should not have conventional or custom wavefront Lasik, All-Laser Lasik, or Epi-Lasik until the corneal abrasion has healed.
Conventional or custom wavefront Lasik, All-Laser Lasik, or Epi-Lasik all require the use of a microkeratome that can cause a corneal abrasion or exacerbate an existing abrasion. Newer mechanical microkeratomes that use a metal blade exert less lateral stress on the surface of the cornea and are therefore less likely to cause an abrasion. The Intralase femtosecond laser microkeratome induces very little lateral stress on the surface of the cornea and would be less likely to cause a corneal abrasion.
Lens-based refractive surgery techniques P-IOL and RLE do not involve the surface of the cornea in the same manner as cornea-based refractive surgery and do not have the same probability of causing a corneal abrasion, however a distressed epithelium is predisposed to corneal abrasion in all situations. Maladies such as ABMD need to be diagnosed and treated before considering refractive surgery. To avoid corneal abrasions, a detailed examination of the health of the eye performed by a competent eye physician is advised.
People with a corneal abrasion will often complain of pain and foreign body sensation. The eye will often be red. Light sensitivity is often reported. Visual acuity may decrease slightly, greatly, or fluctuate.
There are may very serious maladies of the eye that have the same symptoms of eye pain, redness, sensitivity to light, and decreased vision but are not corneal abrasion. Any person who is experiencing these symptoms should be evaluated by an eye physician.
Although the corneal surface will often rapidly heal on its own, it is very important that an eye doctor carefully monitor the progress of healing. The patient may require antibiotics for the eye or other medications.
For some types of corneal abrasion, PTK is a recommended treatment. PTK is essentially PRK for purposes other than refractive error. For this reason, PRK and its cousin LASEK may (emphasis on "may") be appropriate. Similarly, in some instances Epi-Lasik may be appropriate.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgery Doctor.
LASEK: Comparison to Lasik, All-Laser Lasik, Epi-Lasik, and PRK
LASEK:Comparison to Lasik, All-Laser Lasik, Epi-Lasik, and PRK
LASEK
Comparison to Lasik, All-Laser Lasik, Epi-Lasik, and PRK
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Laser Assisted Sub-Epithelial Keratomileusis (LASEK) is a refractive surgery technique developed by Italian doctor, Massimo Camellin, MD and first publicized in 1999. The motivation behind LASEK was to find a surface ablation technique like PRK that induced less discomfort, offers a lower incidence of corneal haze, and provides the patient with faster vision recovery time.
To understand LASEK, on needs to understand a little about PRK and conventional or wavefront custom Lasik.
Hazy View of Things
A major problem with PRK in its early development was corneal haze. Corneal haze is caused by the cornea’s wound response. Surgery is an insult to the cornea, and your cornea really doesn’t care if you want this insult, it is going to respond as if it has been wounded. A part of that wound response causes opaque cells to form. This presents as white hazing of the cornea, restricting light from passing through, and reducing the quality of vision.
Combine Old With New
It was noted that wound response to PRK laser ablation deeper in the cornea is significantly different than when the ablation is performed at the outer surface of the cornea. The idea was formed to creating a flap of corneal tissue using ALK methods, perform the PRK ablation under the flap and deeper in the cornea, then returning the flap over the ablated area. Thus Lasik was created as a combination of ALK and PRK. Lasik literally “fools” the cornea into not knowing it has been wounded. This is why Lasik normally provides virtually no pain, has an almost instant vision recovery, and almost never causes corneal haze; the cornea almost doesn’t know it has had surgery.
Moderate Correction = No Haze
PRK haze does not normally form for corrections that require a moderate amount of tissue removal, generally less than about 6.00 diopters of refractive error. That is good news for moderate and low myopia (nearsighted, shortsighted) and virtually all hyperopes (farsighted, longsighted), but bad news for those needing higher corrections. As a general rule, if you need less than 6.00 diopters of correction, LASEK will not offer a risk of corneal haze any different than PRK. Above 6.00 diopters, LASEK may have an advantage.
Old Reliable Vitamin C
It has been found that having a patient take 500mg of vitamin C (yes, plain old vitamin C) twice a day for a week before PRK and at least two weeks after surgery significantly reduces the incidence of corneal haze. Isn’t it always the simple answer that is the best. This appears to be helpful, but more study is needed to determine just how much help is provided with oral vitamin C supplements. It is really not known if vitamin C is enough for someone who needs 8.00 diopters of correction, but is not enough for someone who needs 10.00. The limits need to be determined.
Strong Medicine
The use of the topical eye drop Mitomycin C dramatically reduces the probability of haze, and can be used to treat haze when it occurs, but this is rather strong medicine. Mitomycin C is appropriate when required, but probably needs to be avoided if possible. Also, Mitomycin C changes how much tissue the laser ablates with each pulse, so the doctor needs to manually change the treatment plan. This requires additional expertise.
It's All In The Flap
The concern between LASEK and Lasik is the Lasik flap. Although it provides the patient with more comfort, virtually eliminates the probability of haze, and offers very quick visual recovery, if the flap exists, there will be the possibility of flap related problems. Those potential problems do not stop when you leave the surgery suite. Once you have had Lasik you have always had Lasik and you must always consider that your eye is fundamentally and forever changed. Change can be a good thing, but sometimes not.
Another potential problem with Lasik is that severing the corneal nerves deeper in the cornea often will temporarily induce dry eyes. The signals from the cornea are interrupted until sensation returns with healing. That can be weeks to months. Although fewer than 3% of refractive surgery patients have any kind of unresolved complication at six months postop, dry eyes is the temporary problem most prevalent with Lasik.
Yet another issue with the thicker Lasik flap relates to the ability to create more detailed ablation profiles with newer technology like flying spot gaussian beam excimer lasers and wavefront-guided ablations. The wavefront ablation profile of where more tissue needs to be removed here, and less tissue needs to be removed there, is very nuanced with tiny changes across the treatment area. The limitation with Lasik is that you are putting a relatively thick 100-180 micron flap of corneal tissue on top of this fancy nuanced ablation. Like too many blankets on the bed, you lose some of the detail of the shape of who is in that bed. Also, the Bowman’s layer and uppermost layer of cells of he cornea are more dense than the deeper stromal layer. It is opined that ablation in Bowman's layer may help in creation of better and better ablations.
And if that was not enough, the Lasik flap is from 100 to 180 microns thick. If the patient has a thin cornea, there may not be enough room for the Lasik flap, the tissue ablation, and the 250 microns of untouched cornea that is needed to keep stability and reduce the probability of ectasia.
A Flap That's Not A Flap
The desire to eliminate potential Lasik flap related problems brings us back to PRK, but PRK is not terribly comfortable for the patient, has a longer recovery period, and there is that problem with haze for higher myopes. The idea that Dr. Camellin had was to create an "epithelial flap" that would fool the cornea the way the thicker Lasik stroma flap does, but not be subject to the same complications as a Lasik flap.
During PRK, the epithelium is removed and the excimer laser treatment occurs on the underlying outermost surface of cornea. Rather than removing the epithelium, LASEK attempts to save the epithelium by using an alcohol solution to cause the epithelial cells to weaken. After removing the solution from the eye, the doctor will lift the edge of the weakened epithelial flap and gently fold it back out of the way. The corneal epithelial cells are the fastest reproducing cells in the human body. Even if destroyed by the alcohol solution, they will quickly regenerate. After the epithelial flap is moved out of the way, excimer laser energy is then applied through the Bowman's Layer and into the upper stroma to reshape the cornea. When the cornea has been reshaped by the laser, the epithelium flap is returned back to its original position.
A contact lens is placed on the cornea shortly after surgery as a bandage for several days to aid in the healing and the reduction of pain. It normally takes three to ten days for the epithelium to heal and resurface the cornea. This healing time varies depending on a number of factors such as the size of the area treated, the health of the patient's cornea, the individual's in healing rate, and the toxicity of the medications and solutions applied to the surface of the cornea.
Neither a mechanical nor laser microkeratome is used in Lasik is used in LASEK.
LASEK Flap Loss Means PRK
Sometimes when LASEK is attempted, the 50-micron thin epithelium flap is not strong enough to be laid back over the treatment zone. In these cases, the epithelium will be removed as it would have been in PRK. In this situation the LASEK procedure becomes a PRK procedure. If this happens and the patient was within the parameters for PRK, there is no cause for concern because it will normally not adversely affect the visual result. If the patient was a high myope and LASEK was being used as a technique to reduce the probability of corneal haze, then there may be a problem. Most doctors will tell a LASEK patient that LASEK will be attempted but it cannot be guaranteed that the LASEK will be completed - the epithelium of each individual behaves differently.
Advantages and Disadvantages
Visual recovery after LASEK is generally faster than in PRK, a little slower than Epi-Lasik, but significantly slower than Lasik.
The potential advantages of LASEK over PRK are a reduction of postoperative discomfort, a decreased risk of infection, and decreased incidence of corneal haze. Advantages of LASEK over Lasik include elimination of the possibility of any stromal flap complications during surgery or throughout the patient's lifetime, including striae, DLK, and others, a decreased risk of temporary induced dry eyes, and an increase in the overall thickness of the untouched area of the cornea. Advantages of Lasik over LASEK include virtually no pain with Lasik and almost instant clear vision, often called the "WOW!" effect.
A progression of LASEK is Epi-Lasik. Epi-Lasik uses a mechanical microkeratome with a blunt blade to slide across Bowman's and lift up a flap of epithelial cells. This flap is not reduced in strength by an alcohol solution and tends to be more stable than a LASEK flap.
The use of the excimer laser for LASEK is not FDA-approved, but is an accepted "off label use" use of the excimer laser. Lasik was also an off label use of the excimer laser for many years and with some lasers continues to be an off label use.
As with nearly all excimer laser based refractive surgery, correction can be performed with both conventional ablation and wavefront-guided ablation.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgeon.
Video courtesy University of Illinois Eye & Ear Infirmary.
All-Laser Lasik - IntraLasik
All-Laser Lasik - IntraLasik
Detailed comparison to traditional Lasik.
 The femtosecond laser creates a series of bubbles within the cornea that when combined make the Lasik flap. Click for video. |
All-Laser Lasik may be performed with conventional laser ablation or wavefront-guided custom Lasik laser ablation.
There are several advantages to All-Laser Lasik that can make All-Laser Lasik more predictable and safer than traditional Lasik with a mechanical microkeratome, however there are limitations and a unique set of concerns that need to be evaluated.
Advantages include more precise positioning of the flap, more accurate thickness of the flap, more even thickness of the flap throughout, and a lower probability of intraoperative complications such as buttonhole flaps, thin/thick flaps, or epithelial defect. Recent studies have shown All-Laser Lasik to be more favorable than Lasik with a mechanical microkeratome in providing vision with better contrast sensitivity.
Some patients, but not all, experience a short period of increased corneal edema with All-Laser Lasik. This slight swelling can cause vision to be blurry, but the swelling normally resolves with healing. Occasionally an All-Laser Lasik patient will experience some photosensitivity. All these issues usually resolve during the normal Lasik six-month healing process, however additional eye drop medication may be required.
All-Laser Lasik is an option for nearly all who decide to have refractive surgery with a corneal flap, but All-Laser Lasik may be a requirement for individuals with preexisting epithelial defects, large pupils, thin corneas, poor contrast sensitivity, or other physiological reasons that indicate the greater accuracy and safety of All-Laser Lasik is required.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgery Doctor.
If this article did not fully answer your questions, use our free Ask Lasik Expert patient forum.
Wavefront Custom Lasik Laser Eye Surgery
Wavefront Custom Lasik Laser Eye Surgery
CustomVue, CustomCornea, Zyoptix, or Allegretto for Lasik, All-Laser Lasik PRK, LASEK, and Epi-Lasik.
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WaveLight Allegretto
Visx CustomVue
LADARVision CustomCornea
Bausch & Lomb Zyoptix
Learning if you would do fine with conventional refractive surgery or if you require wavefront custom Lasik, All-Laser Lasik, LASEK, PRK, or Epi-Lasik is much easier than it may at first appear, however it is important to understand what wavefront custom Lasik, LASEK, PRK, and Epi-Lasik is, and what it is not. As a general rule, the quality of vision with wavefront is superior to conventional laser eye surgery, but that does not mean that wavefront Lasik is best for everybody. Individual circumstances will vary.
The primary difference between conventional Lasik and wavefront custom Lasik is the mapping system that guides the laser. Wavefront can be used for virtually all laser eye surgery techniques including All-Laser Lasik, Lasik, PRK, LASEK, and Epi-Lasik.
Old Science, New Application
Wavefront is a very old technology that has only recently been applied to human vision. Wavefront has been used for years by astronomers who need to adjust the optics of their telescopes. A reflecting mirror within the telescope that can be deformed is adjusted using wavefront data to eliminate aberrations induced by the Earth's atmosphere. In wavefront custom Lasik, PRK, LASEK, and Epi-Lasik, the excimer laser uses wavefront information to change the shape of the cornea by ablating tissue.
Wavefront Diagnosis and Wavefront Treatment
Wavefront is actually used in two separate ophthalmic events. The first is a wavefront evaluation and diagnosis of existing aberrations. The second is using what is learned from the diagnosis to create a wavefront-guided ablation for Lasik, PRK, LASEK, or Epi-Lasik.
Our organization has included wavefront diagnostic as a must-do in our 50 Tough Question For Your Doctor, but we have not included it for guided ablations. A wavefront diagnostic can determine if an individual has aberrations that would be exacerbated by refractive surgery to the point of causing vision problems. No other technology can achieve this level of diagnosis. Wavefront diagnostic can determine if a wavefront guided ablation is an absolute requirement, conventional ablation would be fine, or the patient should not have surgery at all. This is why we believe wavefront diagnostic is an important evaluation.
Several Laser Options
In the United States, there are four wavefront responsive laser manufacturers. The trade names are CustomCornea using the Alcon LADARVision laser, CustomVue using the Visx S4 laser, and Zyoptix using the Bausch & Lomb Technolas 217z laser. These three have the ability to create an ablation customized from an individual patient's wavefront evaluation.
The Wave Light Allegretto laser used wavefront derived data in the laboratory to optimize its laser ablation pattern, but does not use an individual patient's wavefront diagnosis to create a customized ablation pattern. CustomVue, CustomCornea, and Zyoptix are all customized to the individual's eye. Visx, Alcon, and B&L refer to their systems as "custom wavefront". Allegretto is referred to as "wavefront optimized".
Square Grid In, Wavy Grid Out
During a wavefront diagnosis, light is sent into the eye in a specific pattern, then measured after it has passed through the visual system. Any difference between what goes in and what is measured is considered an aberration. Think of a square grid going in and a wavy grid coming out. The waves represent aberrations.
Higher Order Aberrations
A common eye examination and refraction evaluates low order aberrations (LOA). These are commonly called sphere (myopia, nearsighted, shortsighted or hyperopia, farsighted, longsighted) and cylinder (astigmatism). Only a wavefront diagnosis is able to measure high order aberrations (HOA), which are beyond simple sphere and cylinder. HOA are represented in mathematical calculations and are therefore infinite. The more common of these mathematical calculations are Zernike polynomials and have names like spherical aberration, coma, trefoil, and quatrefoil. Ophthalmology only deals with about the first eight levels of HOA as represented in Zernike.
Wavefront technology as a diagnostic device is unsurpassed. This technology can diagnose and measure aberrations that no other system can even see. It is important to understand that without a wavefront diagnosis, it is impossible for a doctor to accurately determine if wavefront-guided ablation is necessary for a good Lasik, PRK, or LASEK outcome. Also, without a wavefront diagnosis it is impossible for a doctor to accurately determine if a wavefront ablation is not necessary. In other words, virtually every person considering Lasik, LASEK, PRK, or Epi-Lasik should have a wavefront diagnostic evaluation.
Detailed Mapping
Think of an eye examination as a way to "map" vision limitations. A conventional eye exam can map LOA. A wavefront diagnostic can map LOA and HOA. Laser eye surgery based upon the LOA determined with a conventional eye exam is like using a map of your state to find your way around. That works pretty well if you are trying to get from Los Angeles to San Francisco. Custom wavefront could be compared to a map of your city. It can help guide you to a specific street corner. Custom wavefront-guided Lasik, LASEK, PRK, and Epi-Lasik directs the excimer laser to change the shape of the cornea using a more detailed mapping system than conventional refractive surgery.
Human vision provides some unique challenges for application of wavefront technology. The human eye is not a telescope. The eye is dynamic, with ever changing focus, pupil size, and other normal biological fluctuations. A telescope is static and once adjusted for a certain set of aberrations, never changes. A deformable mirror can be adjusted to a very precise amount. Ablating corneal tissue is not nearly so precise. Wavefront may be an excellent mapping system, but that does not necessarily mean that you can get to where you want to go.
HOA are divided into separate terms and some HOA are much more important to good quality vision than others. Spherical aberration, coma, and trefoil are examples of HOA that are very important to keep low. An HOA measurement often used is Root Mean Squared (RMS). RMS is more or less an average of all HOA. Having a low RMS is good, but if you have an elevated HOA that is one of those that is known to cause vision quality problems, a low average may not be enough. As an example, if you have low HOA RMS, but a high spherical aberration, wavefront-guided surgery may be a requirement. You will need to discuss this issue in detail with your doctor. Wavefront-guided refractive surgery is FDA approved for a wide range of correction, but this is a range that does have limits. If you are too myopic, too hyperopic, or have too much astigmatism, you may not be eligible for wavefront-guided Lasik, PRK, LASEK, or Epi-Lasik.
Ablate Deeper
Wavefront-guided ablations may remove more tissue than conventional ablations, depending upon the unique circumstances of the individual patient. If you have thin corneas, additional tissue removal may be an issue. For more information, see Thin Cornea.
The size of the fully corrected optical zone is limited for wavefront-guided ablations. If your naturally dilated pupils are unusually large, you may have an increased risk of poor vision in low light environments. See Lasik and Pupil Size
Monovision Limitations
If you are considering monovision correction, it will may be necessary to use conventional Lasik, PRK, LASEK, or Epi-Lasik rather than wavefront-guided. Current wavefront-guided lasers are very limited in their ability to undercorrect. It's full correction or nothing at this time. While the non-dominant eye will need to be undercorrected with a conventional ablation, the dominant eye may be fully corrected with a wavefront-guided ablation. Undoubtedly, each of the manufacturers will eventually allow their lasers to undercorrect in wavefront-guided mode.
Better, Not Perfect
Something very important to understand is that not all aberrations are reduced with custom wavefront or wavefront optimized Lasik, PRK, LASEK, or Epi-Lasik. In fact, in all refractive surgery procedures, wavefront or conventional, HOA tends to increase. This is one of the reasons that the FDA has approved the use of wavefront-guided ablations, but has not specifically approved any laser to actually treat and reduce HOA. Our organization distributed a special Advisory Memorandum regarding this issue. See FDA HOA Advisory.
It has been shown, however, that CustomVue, CustomCornea, and Zyoptix increase HOA less than conventional ablations. This is also true of Wave Light. HOA may increase no matter what you choose, but it will probably increase less with wavefront. Because HOA is likely to increase, if your natural HOA are already elevated, refractive surgery may elevate them farther and cause poor vision. In this situation, it may be that no corneal-based refractive surgery is appropriate.
Get Out Your Credit Card
Let's not forget cost. Many doctors charge more for wavefront-guided refractive surgery than conventional. Although no one should compromise their vision for a little cost savings, paying less for surgery is usually preferred over paying more.
If you meet all other requirements, there is nothing that indicates wavefront-guided Lasik, LASEK, PRK, or Epi-Lasik will provide an outcome that is inferior to similar conventional surgery, and there are many indications that wavefront-guided surgery will provide a superior outcome. However, there are absolutely no guarantees in surgery and refractive surgery is no exception. Any prediction of your actual outcome will be based upon past experience and reasonable evaluations, but no one will know for sure until after surgery. You may want to see Lasik Outcomes.
Wavefront Diagnostic For Every Patient
Everyone considering any corneal-based refractive surgery, such as Lasik, LASEK, PRK, or Epi-Lasik should have a wavefront diagnostic. A wavefront diagnostic will determine if critical HOA are below normal, normal, or elevated. If the HOA are elevated, either wavefront-guided surgery is required, or no surgery is appropriate. If HOA are normal, wavefront-guided surgery may be wise. If HOA are below normal, wavefront-guided continues to be an option, but not a requirement. This is assuming, of course, that you meet all other requirements for wavefront-guided Lasik, LASEK, PRK, or Epi-Lasik laser eye surgery.
If you are ready to choose a doctor to be evaluated for conventional or wavefront custom Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgeon.
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