LASIK, PRK, RK and Vision Correction Surgery
Introduction
Many people who have substandard vision find the inconvenience of wearing contact lenses and/or glasses bothersome. Some pilots, rightly or wrongly, feel their chances of being hired by a major commercial airline are reduced if they wear glasses. Others may choose not to wear glasses for appearance or image reasons. Athletes engaged in sports and water sports or in windy environments may not find contact lenses suitable for their sport.
Advances in ophthalmologic surgery have given some visually deficient people the opportunity to enjoy near normal distant vision without corrective lenses. Advertising by eye centers inundates all forms of the media now. The various techniques and claims may be very confusing to the lay person. The pilot or controller is also concerned with the implications for medical certification if he or she were to undergo one of these procedures. What is the true story?
Refractive Errors
Errors in refraction causing impaired visual acuity arise from abnormalities in the anatomy of the eye. These errors are in either the cornea of the eye or from the length of the globe of the eye. Until recently, glasses and contact lenses to compensate for corneal abnormalities were the only option to correct these conditions.
A type of contact lens program to temporarily alter the shape of the cornea, called Orthokeratology (orthoK), is also used. This did not allow permanent freedom from corrective lenses as the molded cornea would gradually return to its original shape. The FAA originally did not allow pilots to correct their vision using Ortho-K lenses, except for the condition known as keratoconus. In January 2004, the FAA removed its restriction on Orthokeratology contact lenses and flying. If a pilot undergoing Ortho-K presents for a FAA medical examination and meets the vision standards using Ortho-K lenses, the pilot may be issued and medical certificate with the limitation “Must wear contact lenses as prescribed. Must have in possession glasses to correct for distant vision.” The FAA requires that the airman wear the Ortho-K lens while performing flight duty.
Refractive Surgery
Research in the former Soviet Union evaluated the possibility of surgically altering the shape of the cornea to give improved vision without corrective lenses. The science and art of refractive surgery has rapidly evolved.
Four basic surgical techniques are currently used to change the shape of the cornea. The earliest technique developed is the Radial Keratotomy (RK). A variation of this procedure is call the Astigmatic Keratotomy (AK). Later, techniques using laser to remove portions of the cornea were developed. The Automated Lamellar Keratoplasty (ALK) which used a manual technique to shave the cornea. The initial laser technique is called Photorefractive Keratotomy (PRK). A refinement of this technique now widely used is Laser Assisted In-Situ Keratomileusis (LASIK). Newer techniques include the use of implantable intracorneal rings and artificial intraocular lenses. A relatively newer technique for correcting farsightedness is Conductive Keratoplasty. Wave-front technology is also a new technique to correct refractive errors of not only the cornea, but also those generated from the lens to the retina.
None of the procedures mentioned corrects for the age related changes in vision, termed presbyopia, and may make the need for reading glasses arise sooner in previously nearsighted individuals. One technique, termed monovision refractive surgery, corrects one eye for distant vision and the other eye for near vision. The FAA has approved monovision refractive surgery for pilots, after a six month adjustment period to the surgery. This procedure has not been approved for controllers. They do not correct other vision problems such as Age Related Macular Degeneration, glaucoma, cataracts, retinal detachments and blindness due to diabetes or trauma.
Radial Keratotomy
Radial keratotomy (RK) attempts to change the shape of the cornea by making radial cuts in the periphery of cornea. The radial cuts have a similar appearance to spokes of a bicycle when looking directly at the cornea. These cuts tend to flatten the cornea and correct myopia or nearsightedness. Generally, RK involves making four to sixteen radial incisions depending on the amount of flattening desired. By making curved corneal incisions, some degree of astigmatism (irregular curvature of the cornea) may also be corrected. This is known as Astigmatic Keratotomy. The cuts are usually made with a scalpel after mapping of the cornea determines the amount of flattening desired. Generally, only one eye is done at a time to allow healing and pain relief, since the eye is usually patched after surgery. RK is rarely performed today in the U.S. because of the significant risks involved and newer techniques available, such as PRK, LASIK, intracorneal rings and possibly, phakic intraocular lenses.
Potential problems with RK exist, particularly for the pilot. The cuts of RK extend from the surface of the cornea through up to 90% of the corneal thickness. This causes scarring as the corneal heals. The scarring may cause disturbances in peripheral vision or a glare phenomenon, particularly at night. The cornea is also weakened and may be subject to rupture with trauma. The military is concerned with the effects of this weakening under high G environments. Consequently, the military does not approve RK in its pilots. The visual acuity following surgery may not stabilize for up to 6-12 months although most surgeons expected stabilization within 3 months.
Most frustrating, however, was the inability to consistently correct to 20/20. Although many surgeons were able to claim that their patients no longer needed to wear glasses when driving, this is because most states only require 20/40 vision or better to drive. For first or second class FAA medical certificates, the pilot still required glasses to fly. In some studies, approximately 85 % of RK patients could see 20/40 or better, but less than 60% could achieve 20/20 vision without correction. Additional surgery or “revisions” attempted to improve on the vision, but increased the complications of scarring, glare and weakening of the cornea.
Some civilian pilots were permanently disqualified from flying because of their inability to correct to 20/20 after RK revisions and their fluctuating vision. Some surgeons attempted to “overcorrect” the refraction by making more or deeper corneal incisions. This would flatten the cornea more than what was needed with the expectation that as the cornea stabilized, it would assume the shape required for 20/20 visual acuity without correction over the following months. The pilot could not fly until the vision stabilized and still may require glasses.
Anatomy and Physiology of the Cornea
The cornea is a clear, living structure of evenly layered cells that is transparent unless it is injured. Because light must pass through the cornea unobstructed, blood vessels are not found in the cornea. Since it is composed of living cells, oxygen must be supplied by diffusing from the air into the cells of the cornea. This oxygen diffusion requirement limited the duration of use of contact lenses drastically with the original hard lenses. The evolution of gas permeable and hydrophilic lenses of today allow much more diffusion of oxygen into the cornea while wearing lenses. The cornea has a firm outer covering called the epithelial layer and a softer inner portion termed the intraepithelial layer. Just like skin, the cornea can heal when damaged, but may scar with deep damage.
Aviation Careers after RK
Radial Keratotomy is fairly easy to detect by any physician or optometrist with a simple ophthalmoscope. This surgery remains disqualifying for entry into military flying programs. It was also disqualifying for hiring by many of the commercial airlines, even if reported to and approved by the FAA, until 1993. The Americans with Disabilities Act of 1993 led most airline medical departments to drop their hiring prohibition against pilots with previous RK. This assumes the pilot’s vision is 20/20 or better, with or without correction, following surgery. As stated above, military aviators are not authorized to undergo this form of refractive surgery.
Automated Lamellar Keratotomy (ALK)
ALK also involves the careful use of a knife-like microkeratome to shave layers off the cornea to change its shape. The surface of the cornea is initially lifted off in a flap. The inner layer of the cornea is then shaved with the microkeratome. Depending on the depth of the cut, both myopia (nearsightedness) and hyperopia (farsightedness) can be corrected using this technique. After the shaving of the cornea, the epithelial flap is then replaced on the cornea and heals without sutures. The complications of ALK include glare, over- or under-correction and corneal scarring or loss. ALK is very similar in principle to LASIK, but uses a microkeratome (miniature knife blade) rather than a laser to shave the corneal stroma.
Laser Techniques
Significant improvements in refractive surgery appeared with the advent of laser techniques. Both PRK and LASIK use a laser to alter the shape of the cornea. A topographic map of the cornea is developed initially. This map measures the refractive power of all portions of the cornea and defines both astigmatism and refractive error. Calculations are made regarding where and what thickness of cornea needs to be removed to give normal vision. The eyes are anesthetized with drops and paralyzed to prevent movement during the surgery. Recovery times and stabilization of vision varies with the technique.
Laser Techniques – Photorefractive Keratotomy PRK
Photorefractive keratotomy uses an eximer laser to reshape the cornea. The procedure was approved by the FDA for use in the US in 1995. In PRK, a laser projected on the eye shave off layers of the epithelium (surface) of the cornea where the curve is excessive. Usually, less than 15% of the corneal thickness is removed. The procedure usually takes about 15 minutes. Most ophthalmologists only perform PRK on one eye at a time to allow healing. The eye is protected with an ointment and may be patched overnight. Anesthetic eye drops are given for pain relief. Vision usually is stable within several weeks, but some change may occur over the following months. The side effects include light sensitivity, glare, central vision haziness and halos.
Laser Techniques – Laser Assisted in-Situ Keratomileusis (LASIK)
Laser in-situ keratomileusis (LASIK) combines the techniques of the ALK and the PRK. Instead of shaving the corneal surface with the laser as in PRK, the LASIK avoids the surface of the cornea and shaves the inner layers (intraepithelial) of the cornea. To do this, the ophthalmologist must initially make an incomplete circular incision near the periphery of the cornea. The surface of the cornea is then peeled back in a flap exposing the intraepithelial layers. The laser is then used on only the intraepithelial layer of the cornea. When the laser “shave” is complete, the corneal epithelial flap is replaced to cover the lased site. Vision may be near normal in one to three days. The complications of LASIK are similar to PRK. Because of the technique used, some people refer to the LASIK as the “flap and zap”.
Conductive Keratoplasty
A new technique to correct farsightedness uses radio waves, rather than the light waves of lasers, to change the shape of the cornea. Heat-causing radio waves from a probe the size of a human hair cause portions of the cornea to shrink. Although the FDA has approved the technology, visual regression may occur for up to one year after the procedure. By comparison, vision stabilizes within 3-6 months following laser procedures.
The FAA approved this procedure in the Summer of 2005. The official protocol unfortunately requires an observation period while grounded for six months followed by possible medical flight test before returning to flying.
Intracorneal Rings
A newer FDA approved vision refraction correcting surgery uses partial rings implanted in the cornea to correct vision errors. Intacs, by KeraVison, were approved on April 9, 1999 by the FDA for non-laser surgical correction of myopia (nearsightedness). A note from the American Society of Cataract and Refractive Surgery states “Intacs were approved by the FDA in 1999 for the correction of mild myopia (up to 3 diopters) without significant astigmatism (less than 1 diopter).” Intacs are tiny plastic (polymethylmethacrylate – PMMA) ring segments that are implanted in the peripheral cornea. Even though they are very small, their mass is enough to change the shape of the front surface of the eye and correct refractive error.
In data from clinical trials presented to the FDA, 98% of patients within the recommended prescribing range could see 20/40 or better one year after the procedure; 78% could see 20/20 or better and 56% could see 20/16 or better. About 7% of patients experienced visual symptoms such as glare or fluctuating vision after the surgery. Complications from surgery included infection (0.2%), too shallow placement of the intracorneal rings (0.2%), anterior chamber perforation (0.4%) and temporary loss of two lines of best corrected visual acuity (0.2%). The rings are removable and the individual’s eyes will return to their pre-operative near-sighted condition.
The intracorneal rings may also be used to correct keratoconus, a condition of the cornea with thinning and irregularity of the surface. Individuals with keratoconus are not candidates for other forms of refractive surgery.
The FAA will allow pilots who have had corneal ring implantation to fly after their vision has stabilized following surgery, just as with PRK and LASIK. Reporting on FAA Form 8500-7, Report of Eye Evaluation, is required at the next FAA physical or sooner.
Phakic Intraocular Lenses
Refractive vision surgical correction may not only involve changing the shape of the cornea, but also adding an artificial lens similar to the method of removing a cataract affected lens and replacing it with a plastic intraocular lens which is so common today. The major difference between the cataract correction procedure and the refraction correction is that in the later, the individual’s own lens would be left in place and an artificial lens would be placed behind the natural lens. This would allow the individual to maintain some ability to accommodate (shift vision focus between near and distant) while correcting the deficiency in distant vision.
The risks associated with this procedure are potential damage to the inner aspect of the cornea, glaucoma, retinal detachment and cataract formation. The advantages include the absence of scarring and swelling of the central cornea with the associated glare and potential loss of 1-2 lines of best visual acuity. This procedure is also reversible.
As above, the FAA will approve pilots having this procedure if their vision meets FAA vision standards after surgery. Reporting to the FAA and clearance is required.
Investigational Technologies
New investigational technologies are looking at correction of hyperopia (farsightedness) through the use of lasers or radio frequency waves to heat the cornea. These techniques are called Laser Thermal Keratoplasty and Radio Frequency Keratoplasty.
Risks
None of these procedures are risk free. Complications can occur that permanently affect vision and may disqualify a pilot. Persons considering these procedures should consult an ophthalmologist with considerable experience, usually more than 500 previous cases. Prices vary widely and may not be covered by insurance. The rage of prices is coming down as competition increases but experience in the procedure is a valuable asset. Expect to pay from $1000 to $3500 per eye at current rates.
A significant disadvantage of laser vision correction techniques is the potential loss of one or two lines on the vision chart of best corrected visual acuity. For example, assume a pilot/controller has 20/200 uncorrected distant vision that corrects with glasses to 20/17 (better than “normal”). Following laser surgery, the uncorrected (no glasses or contacts) vision may have improved to 20/20, but glasses do not improve the vision any further because of the central haziness. This represents the loss of one line of best visual acuity on the eye chart. A loss of two lines would bring the pilot’s best visual acuity to 20/25, which does not meet the FAA standards for 1st or 2nd class medical certification. In both cases, the individual may note a relative decrease in best vision, particularly when scanning for aircraft in the distance. Current studies show that 5% of LASIK patients lose two or more lines of best visual acuity following surgery, but fewer than 0.5% have best corrected visual acuity of 20/40 or less, the FAA Third Class vision standard at distant.
Another potential disadvantage of laser eye surgery is the possible decrease in night vision. Preliminary studies conducted in Great Britain indicate that 30-60% of individuals with moderate to severe myopia prior to surgery had significant decrease in night vision following surgery. Night visual acuity is measured by assessing contrast sensitivity. Please note that this article was written by a strong opponent of refractive eye surgery and not published in a scientific journal. Most ophthalmologists report very few problems with loss of night visual acuity, other than the glare and flare phenomenon.
Relative Advantages
The advantages of PRK and LASIK over RK include more precise correction of refraction and astigmatism, less scarring, glare and weakening of the cornea due to thinner layers of cornea affected, quicker healing and less discomfort. The LASIK has the added advantages of minimal central haziness since the epithelium is intact and the ability to perform the procedure on both eyes at once. An outcome closer to 20/20 is expected and no “overcorrecting” for future remolding of the cornea is required. Revisions are possible, but less common. The potential downside to LASIK is flap instability persisting for extended periods of time.
FAA Policy on Vision Correction Surgery
The FAA will allow pilots to fly following these procedures. With the noted exceptions, controllers may also perform safety sensitive duties following vision correction surgery. Once the vision is stabilized (at least two exams a week apart without changes in acuity), the pilot/controller should have the ophthalmologist complete FAA Form 8500-7, Report of Eye Evaluation. If the vision corrects to 20/20 and there are no complications from the procedure (corneal scarring, night glare, haziness of vision, fluctuating visual acuity), pilots may return to flying and report the surgery at the time of their next FAA physical. The FAA has published conflicting guidance in their educational pamphlet for Lasik and the AME Guide regarding return to flying. In fact based on a narrow interpretation of the FAA policy in the AME Guide, some companies still require reporting the surgery to the FAA and obtaining written clearance prior to flying. Because of conflicting guidance, AMAS recommends airmen clear with their Aviation Medical Examiner before returning to flying after refractive surgery. Controllers are advised to discuss the procedure with the Region Flight Surgeon (RFS) prior to surgery, and will require specific clearance from the RFS before returning to controlling.
A potential problem is the pilot’s original medical certificate still bears the limitation “Must wear corrective lenses.” A ramp check by an FAA inspector may be awkward, even though the pilot meets the FAA standards for vision without correction. The inspector has no way of verifying that fact and may issue a violation. Although the chances are the situation may ultimately be resolved in favor of the pilot, avoiding these administrative hassles is better
Two options exist in this situation. First the pilot can continue to carry glasses when flying until the next medical certificate is issued without any vision limitations. The other solution is to complete the FAA Form 8500-7 and mail it to the FAA. The FAA will respond with a letter acknowledging that the vision limitation is no longer required on the medical certificate. This may take several weeks, but will make the next physical exam much more straightforward with the AME. The pilot will be able to present the letter from the FAA to the AME removing any doubts about whether the AME can issue a medical certificate. The AME who is not certain may defer the medical to the FAA and leave the pilot without a medical for several months while awaiting a decision and processing by the FAA. For the professional pilot, this may have disastrous financial implications. When those circumstances are anticipated, AMAS can report the procedure directly to the FAA Aeromedical Certification Division and obtain a letter of eligibility. Once that is complete, the pilot simply writes “previously reported” on the medical application.
The FAA has a policy allowing pilots who receive monovision refractive surgery to fly with glasses that correct for distance and near for the first six months after surgery. After the six month adaptation period elapses, pilots may then fly without glasses, assuming one eye corrects to distant standards and the other eye corrects to near vision standards. However, as noted previously, monovision correction is NOT allowed for controllers. Also the FAA may require a Medical Flight Test at a local FSDO before clearance to return to flying. Also monovision correction with contact lenses is not allowed for aviation duty.
Airline Policies on Refractive Surgery
Most major U.S. carriers now hire pilots who have had refractive surgery. All airlines require the pilot to have visual acuity, corrected or uncorrected, that meets the FAA First Class Medical standards, 20/20 in each eye at distance with or without correction. They also require pilots to have properly reported their surgery to the FAA as noted above.
AMAS Aeromedical Assistance
For a more specific personal explanation to your questions or those concerning aeromedical certification, contact AMAS for a private consultation. For help in reporting treatment for and obtaining clearance from the FAA to fly or control with these conditions, refer to the AMAS Confidential Questionnaire. If you are an AMAS Corporate Member, these services are FREE to you.