What is Refractive Error?

Approximately 150 million Americans use some type of ophthalmic device to correct refractive error. Refractive error is a visual condition in which light rays are not brought to a single focus on the retina. They include myopia, hyperopia, and astigmatism.

Hyperopia (farsightedness) is a condition in which light rays are focused behind the retina. The axial length of the eye is usually too short, resulting in near objects appearing fuzzy or blurred.

Astigmatism is a condition in which the curvature of the cornea is irregular, resulting in two images, one of which may or may not be on the retina.

What is Refractive Surgery?

Refractive surgery is surgical intervention to correct refractive conditions. Radial keratotomy (RK) has been performed in the U.S. for about 20 years to correct myopia, astigmatism, and even hyperopia. The surgeon makes spoke-like incisions in the peripheral cornea. If the number, length, and depth of the incisions are appropriate, the resulting change in corneal curvature corrects the refractive error. RK requires a considerable amount of surgical skill.

The Food & Drug Administration (FDA) approved the use of the excimer laser to perform a refractive procedure called photorefractive keratectomy (PRK). PRK alters the curvature of the cornea through a series of laser pulses. The laser emits a coherent beam of light that vaporizes (photoablates) the corneal tissue to a predetermined depth and diameter. There is reportedly little damage to adjacent tissue. The removal of corneal tissue reduces the cornea's curvature, correcting myopia.

Is PRK an Option for Me?

It is estimated that up to 80% of the myopic population may physically qualify as potential PRK candidates. The current selection criteria for candidates are listed below.

Selection Critesria:

• Normal Ocular Health
  
• Age 18 Years or Older
  
• Stable Refractive Error (no noticeable change in the last year) Correctable to 20/40 or Better
  
• Between -1.50 to -7.00 Diopters of Myopia
  
• No Gender Restriction, with the Exception of Pregnancy
  
• Realistic Expectations of the Final Results (with a complete understanding of the benefits, as well as the possible risks)
  
• Pupil Size ( 6mm (in room light)
  
  

Pre-existing Conditions That May Contraindicate PRK:

• Collagen Vascular Disease (e.g., corneal ulceration or melting)
  
• Ocular Disease (e.g., dry eye, keratoconus, glaucoma)
  
• Systemic Disorders (e.g., diabetes, rheumatoid arthritis)
  
• History of Side Effects From Steroids
  
  

Is PRK Safe for Aviators?

Operation of an aircraft is a visually demanding activity performed in an environment that is not always user friendly. This becomes particularly evident if your choice of vision correction is ill-suited for the task. Currently, over 50% of the civil airman population uses some form of visual correction. Aviators considering PRK should know that clinical trials claiming success rates of 90% or higher are based on criteria of 20/40 or better, not 20/20 or better, uncorrected visual acuity.

Some complications of PRK that could affect civilian pilots:

• Long Healing Period
  
• Pain
  
• Glare/Halos/Starburst Aberrations
  
• Under/Over-correction
  
• Recurrence of Myopia
  
• Increased Intraocular Pressure
  
• Corneal Haze
  
• Scarring
  
• Cataracts
  
• Reduced Best Corrected Visual Acuity
  
• Reduced Acuity in Low Light
  
  

PRK may be performed on one eye at a time to assess the results of the procedure and ensure adequate vision during the healing process. (Note: The FDA recommends a 3-month period before a second PRK surgery.) Activities requiring good binocular vision may have to be suspended between surgeries and during the, sometimes extended, healing periods.

Post-PRK patients have complained of glare, halos, and starburst aberrations, which may be the result of postoperative corneal haze that develops during the healing process. Reportedly, symptoms have occasionally lingered longer than a year.

Predictability of the resulting refractive correction is less than exact, particularly for those with more severe myopia. This can lead to under/over-correction of the refractive error. In the case of the latter, premature presbyopia (the need for reading glasses) can result.

In 1 to 3% of cases, loss of best corrected visual acuity (BCVA) can result, due to decentered ablation zones or other surgical complications. (Note: Loss of BCVA is reportedly 5 to 15X more likely with PRK than that resulting from the use of extended wear contacts.)

Some PRK patients have reported dissatisfaction with their vision under low ambient lighting (dusk/nighttime) conditions. Pilots who experience postoperative vision problems could be further compromised by the variations in lighting common to the aviation environment. In addition, exposure to intense UV radiation has been associated with late-onset corneal haze and recurrence of myopia.

The FAA will consider applicants with PRK once they are fully healed and stabilized, provided there are no complications and all other visual standards are met. Pilots should be aware, however, that potential employers, such as commercial airlines and private companies, may have policies that consider refractive surgery a disqualifying condition. Also, civilian pilots who wish to fly military aircraft (Army, Air Force, or Naval Reserves) should know that the military does not allow its pilots to have refractive surgery.

In the majority of patients, PRK has proven to be a safe and effective procedure for the correction of myopia. PRK is still evolving with other countries currently using refined techniques and alternative procedures. Many of these procedures are under investigation in the U.S. If you are considering PRK, it is recommended that you contact your eyecare practitioner, who will assist you in making an informed decision concerning the potential benefits and liabilities that may be specific to your situation. Knowing how refractive surgery could affect your visual performance is essential since PRK is NOT reversible!