Photorefractive keratectomy

Preliminary investigation of the corneal topography. The test maps a patient's cornea for raised areas and surface inconsistencies.

LASEK and PRK are two different procedures. While both procedures interact with the epithelium atop the cornea, the PRK procedure removes this entirely, while LASEK brushes the material away for the procedure, before being placed back for healing after laser surgery.[2] The procedure can be used to treat astigmatism, nearsightedness, and farsightedness.[3] During the procedure, the epithelium is displaced using a diluted alcohol solution.[4]

PRK has advantages over LASIK in that it avoids added complications associated with the flap created during surgery. The procedure may also reduce the chances of dry eye symptoms after surgery. Due to the PRK procedure not requiring a surgical flap, athletes or individuals concerned with trauma introduced by the flap may see benefits to LASEK. Patients that wear contact lenses will typically need to stop wearing these for a specified time before the procedure.[5]

PRK disadvantages include a longer recovery time for vision in contrast to LASIK. Another disadvantage is that patient may be required to apply steroid eye drops for a few weeks longer than that of a LASIK procedure.[3] Vision after the PRK procedure has a longer recovery than LASIK which may be between five days and two weeks for blurred vision to properly clear.[4][6]

When LASEK is compared to LASIK, LASIK can have better outcomes with corneal haze while LASEK has a lower rate of flap complications than LASIK.[7]

There are a number of basic criteria which a person should satisfy:

• Normal ocular health
• Age 18 years or older
• Stable refraction error (no noticeable change in the last year) correctable to 20/40 or better
• Between −1.00 to −12.00 diopters of myopia
• Not pregnant at the time of surgery
• Realistic expectations of the final results (with a complete understanding of the benefits, as well as the possible risks)
• Pupil size 6 mm or less in a dark room is ideal (but some newer lasers may be acceptable for larger pupils)
• Assessment of allergies, (e.g., pollen) where allergy may complicate the eyelid margins following surgery leading to dry eye.

There are also some pre-existing conditions that may complicate or preclude the treatment.[8]

• 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
• Granular corneal dystrophy type II

Some complications that can be temporary or permanent include:

• Dry eyes[9]
• Recurrent erosions during sleep
• Long healing period
• Pain[10]
• Glare, halos, or starburst aberrations
• Increased ocular straylight
• Under- or overcorrection
• Recurrence of myopia
• Corneal haze
• Scarring
• Reduced best corrected visual acuity
• Reduced acuity in low light
• Increased sensitivity

A systematic review that compared PRK and LASIK concluded that LASIK has shorter recovery time and less pain.[17] The two techniques after a period of one year have similar results.[17]

A 2016 systematic review found that it was unclear whether there were any differences in efficacy, accuracy, and adverse effects when comparing PRK and LASEK procedures among people with low to moderate myopia.[18] The review stated that no trials have been conducted comparing the two procedures on people with high myopia.[18]

A 2017 systematic review found uncertainty in visual acuity, but found that in one study, those receiving PRK were less likely to achieve a refractive error, and were less likely to have an over-correction than compared to LASIK.[19]

• LASIK
• Alcohol assisted PRK
• Transepithelial PRK (TransPRK)
• ASA (Advanced Surface Ablation) LASEK, which uses Amoils Brush and gas cooling to reduce the pain
• M-LASEK, which Uses mitomycin in an attempt to reduce post-operative haze but is of dubious effectiveness.[20] Possible long-term side effects are unknown.[21]

In the U.S.A. candidates who have had PRK can get a blanket waiver for the Special Forces Qualification, Combat Diving Qualification and Military Free Fall courses. PRK and LASIK are both waived for Airborne, Air Assault and Ranger schools. However, those who have had LASIK must enroll in an observational study, if a slot is available, to undergo training in Special Forces qualification. LASIK is disqualifying/non-waiverable for several United States Army Special Operations Command (USASOC) schools (HALO, SCUBA, SERE) per Army Regulation 40-501.[22]

The U.S. Federal Aviation Administration 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, civilians who wish to fly military aircraft should know that there are restrictions on those who have had corrective surgery. The Army now permits flight applicants who have undergone PRK or LASIK. Uncomplicated, successful corneal refractive surgery does not require a waiver and is noted as information only.[23]

The Navy and Marines will routinely grant a waiver for pilots or student naval aviators, as well as naval flight officers, UAS operators and aircrew, to fly after PRK and LASIK, assuming preoperative refractive standards are met, no complications in the healing process were encountered, asymptomatic with regard to significant halos, glare or dry eye, off all medications, and passing their standard vision tests. In one study, 967 of 968 naval aviators having PRK returned to duty involving flying after the procedure. In fact, the U.S. Navy now offers free PRK and LASIK surgery at the National Naval Medical Center to Naval Academy Midshipmen who intend to pursue career paths requiring good uncorrected vision, including flight school and special operations training.

The U.S. Air Force approves the use of PRK and LASIK.[24] Since 2000 the USAF has conducted PRK for aviators at the Wilford Hall Medical Center. More airmen were allowed over the years and in 2004 the USAF approved LASIK for aviators, with limits on the type of aircraft they could fly. Then in 2007 those limits were lifted.[25] Most recently in 2011 the USAF expanded the program, making it easier for more airmen to qualify for the surgery. Current airmen (Active Duty and Air Reserve Components who are eligible) are authorized surgery at any DOD Refractive Surgery Center. Those airmen not eligible, are still able to get the surgery done at their own expense by a civilian surgeon, but must first be approved (approval is based on the same USAF-RS program[26]). Others that do not fall into those categories (i.e. applicants who are seeking a pilot slot) can still elect to have the surgery done, but must follow the criteria in accordance with the USAF Waiver Guide.[27] Those applicants will be evaluated at the ACS during their Medical Flight Screening appointment to determine if they meet waiver criteria.

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. Given that PRK is not reversible, a patient considering PRK is recommended to contact an eye-care practitioner for assistance in making an informed decision concerning the potential benefits and liabilities that may be specific to them.

The first PRK procedure was performed in 1987 by Dr. Theo Seiler, then at the Free University Medical Center in Berlin, Germany.[28] The first procedure similar to LASEK was performed at Massachusetts Eye and Ear Infirmary in 1996 by ophthalmologist and refractive surgeon Dimitri Azar.[29] Dr. Massimo Camellin, an Italian surgeon, was the first to write a scientific publication about the new surgical technique in 1998, coining the term LASEK for laser epithelial keratomileusis.[30]