Eye Care Options

Refractive surgery has become increasingly popular in the United States in recent years. The goal of refractive surgery is to provide clear distance vision with less — or no — dependence on glasses or contact lenses. Vision is obviously important in all aspects of flying. Aviators frequently ask whether this type of surgery is effective in correcting vision and, of equal importance, if it is permissible for the medical certification of pilots.

To understand how refractive surgery works, we must first review how the eye functions. The cornea, where light enters the front of the eye, together with the lens inside the eye, focuses the light to form an image on the retina at the back of the eye. The cornea provides most of the eye's focusing power, with the lens providing the remainder. If light is focused directly on the retina, then vision is clear. In myopia (nearsightedness), the eye focuses light such that images of distant objects are formed in front of the retina instead of on the retina. Distant images are therefore perceived as being blurred. Myopia affects approximately 25 percent of adults in the United States. Hyperopia (farsightedness) is a focusing error in which images are formed behind the retina, and therefore the image on the retina is again perceived as being blurred. Astigmatism is a very common condition in which the cornea is irregularly shaped instead of spherical. In other words, there is more focusing power in certain areas than in others, and images are distorted. Finally, presbyopia refers to a condition accompanying the normal aging process that results in a degradation of near vision in just about everyone after the age of 35 to 40 years.

Refractive errors, including myopia, hyperopia, astigmatism, and presbyopia, can be corrected by any method that alters the total focusing power of the eye, most commonly with the use of glasses or contact lenses. Refractive surgery works by altering the shape of the cornea, thereby altering the refractive or focusing power of the eye. Currently, refractive surgery is approved by the Food and Drug Administration (FDA) only for the correction of myopia and mild degrees of astigmatism.

There are numerous refractive surgical techniques in use, but the most commonly performed procedures today are radial keratotomy (RK), photorefractive keratectomy (PRK) and, most recently, laser in situ keratomileusis (LASIK).

As long as the visual requirements are met, refractive surgery is approved by the FAA for all classes of airman medical certification. However, because of the many potential side effects and its long-term instability, refractive eye surgery is not currently an acceptable means of visual correction among aviators in the U.S. armed forces. Applicants for flight training in any branch of the military services who have had this surgery will not be accepted. Most commercial airlines are presently reluctant to hire airmen who have had refractive eye surgery. A history of refractive eye surgery must be acknowledged on the medical application, and evidence from previous refractive eye surgery can be easily detected on a complete eye examination. For the professional pilot, refractive eye surgery is not a good option at the present time.

In myopia, refractive surgery reduces the focusing power of the cornea by flattening its central curvature. A flatter cornea has less refractive power than a cornea with a steeper curvature. Images are again focused on the retina instead of in front of it. To correct hyperopia, the central corneal curvature must be steepened. This is much more difficult to accomplish with refractive eye surgery than flattening the cornea. Research trials are currently under way to evaluate the effectiveness of refractive surgical techniques to treat hyperopia, but FDA approval has not yet been granted for treatment of farsightedness outside of experimental tests. None of the refractive surgery procedures eliminates presbyopia, or the need for reading glasses.

During radial keratotomy, the eye surgeon — aided by a microscope — makes multiple radial incisions in the cornea in a spoke-like pattern around the eye (see top photo, p. 103). This relaxes the cornea and alters its shape. The number and depth of the incisions is calculated to flatten the cornea based on the extent of the myopia present. To correct astigmatism, incisions may be curvilinear in shape and may be placed in only certain radials. In photorefractive keratectomy (PRK), a special type of laser, called an excimer laser, is used to remove small amounts of tissue from the front of the cornea. This sculpting of the corneal surface flattens its shape, thereby reducing the degree of myopia. In astigmatic patients, sculpting is done only in certain areas to return the corneal surface to a more optimal round shape. PRK has been approved by the FDA only since 1995 and is approved only for the treatment of mild to moderate degrees of myopia and minimal amounts of astigmatism. The newest procedure is LASIK, in which the outer surface of the cornea is cut and lifted away. The laser beam is then applied to the inner portion of the cornea, after which the surface tissue is returned to its normal position. LASIK is a modification of PRK that may decrease the chance of postoperative scarring and may reduce the incidence of postoperative pain. All forms of refractive surgery take less than 30 minutes per eye to perform, and the surgery is done with only drops to anesthetize the eye. Postoperative pain and discomfort are common for several days after all types of refractive surgery. Vision frequently is hazy or cloudy for as long as six months after refractive eye surgery, although typically this haze disappears over time.

There are numerous well-controlled studies predicting the visual outcome after refractive surgery. In general, results show that between 70 percent and 90 percent of patients have uncorrected vision of 20/40 or better after RK. After PRK, approximately 94 percent of patients have 20/40 or better uncorrected vision, but less than 60 percent have 20/20 or better vision. At this time, there has been no large, well-controlled FDA trial of the newer LASIK procedure published in the medical literature. Smaller, less sophisticated studies seem to suggest that visual results are similar to those seen with the PRK procedure.

Radial keratotomy has been performed on several hundred thousand patients in the United States since the 1970s. Therefore, follow-up data is available on patients who had this procedure more than 20 years ago. Such data is not available — and will not be available for some time — for PRK and LASIK. A study funded by the National Eye Institute assessed the efficacy, safety, predictability, and stability of RK. This study showed that 10 years after having RK, only 50 percent of patients had 20/20 distant vision without glasses or contact lenses, although 85 percent had at least 20/40 uncorrected vision. A significant additional finding was that more than 40 percent of patients had long-term instability of the refractive correction with continued flattening of the cornea resulting in a further shift towards farsightedness 10 years after surgery. In other words, almost half of patients who had RK will notice continued change in their focusing ability as long as 10 years after the procedure.

Complications of refractive surgery are rare but can be significant and need to be fully understood by patients contemplating these procedures. Approximately three percent of eyes undergoing RK develop scarring and permanently lose several lines of vision on an eye chart that cannot be corrected with glasses or contact lenses. A similar three-percent chance of losing several lines of best corrected vision occurs with PRK and presumably also with LASIK but again, no large research studies on LASIK have yet been completed. Although a three-percent chance of losing vision may seem to be phenomenally low, it may be argued that it is an unacceptably high risk for patients with healthy eyes who can see 20/20 with glasses or contact lenses. It is certainly conceivable that a pilot may lose his medical certificate because his vision is no longer correctable to the required level of acuity after refractive surgery.

In a profession where vision standards are required, the risks of refractive surgery may be too great. Other well-known complications or problems that may occur after any refractive surgery procedure include over- or undercorrection. This may require a second refractive surgical procedure, or enhancement, in order to attain the desired result. Even patients who have good vision after surgery may develop other visual disturbances that can interfere significantly with normal visual function. Some of these problems include fluctuations in vision throughout the day, double vision, glare intolerance, seeing star bursts around light sources, and severe sensitivity to bright lights. Another very common complaint after refractive surgery is impairment of night vision. These adverse post-treatment symptoms may occur in up to 10 percent of patients and could interfere with a pilot's ability to function in his profession.

Other complications worth mentioning include a possible increased risk for rupture of the eye with blunt trauma, or a direct hit to the eye, after RK. The incisions in the cornea, even when healed, weaken the structural integrity of the eye, making it more susceptible to serious injury from trauma. Theoretically, the structural integrity of the eye is less altered after PRK or LASIK than after RK, and small trials seem to confirm this theory. Also, small studies have implied that RK should not be performed on persons who spend extended periods of time at high altitude. Patients with RK may notice a strong shift of their refractive error. At high altitudes, persons who have had RK may temporarily become farsighted. Although this is reversible upon returning to lower altitudes, fluctuations in altitude may lead to fluctuating visual acuity. This is obviously a potential problem for pilots. Thus far, this effect has not been detected in patients after PRK or LASIK procedures. A small percentage of patients may also be more susceptible to glaucoma after the procedure. Until further research trials are completed, the long-term safety and potential side effects of PRK and LASIK are not yet entirely understood.

Finally, orthokeratology, a refractive "treatment" not requiring surgery, deserves mention. In the past, this was a very popular method of "treating" defective distance vision among pilots who desired a first or second class medical certificate. Also known as ortho-k, this procedure is highly advertised in professional and other aviation journals as a non-surgical, safe method of restoring 20/20 uncorrected vision. Orthokeratology involves wearing a series of successive contact lenses with progressively different curvatures from that of the cornea. Over several weeks, these poorly fitting contact lenses will mold the shape of the cornea and flatten it temporarily. This allows the patient to have improved uncorrected distance vision for several hours to days (long enough to pass the distant vision test) after removing the contact lenses. Since the cornea will gradually resume its former shape, a "retainer" contact lens must be worn regularly in order to maintain good uncorrected vision without the contact lens. This procedure is not without risks, however. As with any poorly fitting contact lens, there are numerous possible complications, including swelling of the cornea, growth of abnormal blood vessels onto the cornea, infections, and possible scarring. Most ophthalmologists discourage this procedure.

Because the FDA has approved refractive eye surgery, the FAA has also made an allowance for such procedures. An applicant who has been treated with refractive surgery must still meet the usual visual acuity standards of FAR Part 67. In addition, before flying again after refractive surgery, the applicant must have a Report of Eye Evaluation, completed by an ophthalmologist, indicating that healing is complete, that visual acuity is stable, and that no significant side effects are experienced. The typical recovery time before a Report of Eye Evaluation form can be completed is six to 12 weeks after the refractive surgical procedure is performed.

Advancements and refinements in techniques over the years have led to the success of refractive eye surgery. Good uncorrected visual acuity is achieved in ever-increasing numbers, and most patients are happy. Yes, it would be nice to wake up in the morning and not have to grope for a pair of glasses or put in contact lenses. However, patients must understand that refractive surgery permanently alters the optical performance of an otherwise healthy eye, and the changes induced by surgery may allow visual compromise to occur. Many patients, including pilots, have undergone these procedures successfully, and many more will consider them in the future. What is most important is that patients contemplating refractive eye surgery remain informed about all the risks, benefits, and alternatives to these procedures.

Ingrid E. Zimmer-Galler, M.D., is a vitreo-retinal surgeon at the Wilmer Eye Institute of Johns Hopkins Hospital in Baltimore. An instrument-rated private pilot, she owns a V35B Bonanza and is currently restoring a 1939 J-3 Cub.