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Prospective Evaluation of Radial Keratotomy (PERK) Study

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT00000129
Recruitment Status : Completed
First Posted : September 24, 1999
Last Update Posted : September 17, 2009
Information provided by:
National Eye Institute (NEI)

Brief Summary:

To determine whether radial keratotomy is effective in reducing myopia.

To detect complications of the surgery.

To discover patient characteristics and surgical factors affecting the results.

To determine the long-term safety and efficacy of the procedure.

Condition or disease Intervention/treatment Phase
Myopia Procedure: Radial Keratotomy Phase 3

Detailed Description:

Approximately 11 million Americans have myopia that can be corrected with eyeglasses or contact lenses. Some of these people may also be candidates for radial keratotomy (RK), a procedure that aims to correct or reduce myopia by surgery that flattens the corneal curvature.

Keratotomy was first performed by surgeons in Europe and the United States in the late 1800s, and the basic optical and mechanical principles of the operation were defined in the 1940s and 1950s by the Japanese doctors T. Sato and K. Akiyama, who used anterior and posterior corneal incisions. The posterior incisions damaged the cornea, and the procedure was modified in the Soviet Union by doctors Fyodorov and V. Durnev to include incisions in only the anterior cornea. Since its introduction into the United States in 1978, numerous ophthalmologists have modified the procedure by introducing technical and surgical improvements such as ultrasonic methods to measure the thickness of the cornea and the use of diamond-bladed micrometer knives to make the incisions.

However, scientific assessment of RK lagged behind growing public and professional interest in the procedure. In 1980, in response to widespread concern about the long-term safety and efficacy of RK, a group of ophthalmic surgeons approached the National Eye Institute with a proposal for a multicenter clinical trial that would evaluate the potential benefits and risks of this procedure.

The Prospective Evaluation of Radial Keratotomy study, involving 435 patients and 99 pilot patients, was a clinical trial designed to evaluate the short- and long-term safety and efficacy of one technique of radial keratotomy. The procedure was evaluated by comparing a patient's refractive error and uncorrected vision before and after surgery. The more myopic eye received surgery first. Patients were required to wait 1 year before having the operation on the second eye.

The surgical technique was standardized, consisting of eight centrifugal radial incisions made manually with a diamond micrometer knife. The diameter of the central, uncut, clear zone was determined by the preoperative spherical equivalent cycloplegic refraction (-2.00 to -3.12 D = 4.0 mm; -3.25 to -4.3 D = 3.5 mm; -4.50 to -8.00 D = 3.0 mm). The blade length, which determined the depth of the incision, was set at 100 percent of the thinnest of four intraoperative ultrasonic corneal thickness readings taken paracentrally at the 3-, 6-, 9-, and 12-o'clock meridians just outside the mark delineating the clear zone. The incisions were made from the edge of the trephine mark to the limbal vascular arcade and were spaced equidistantly around the cornea.

Patients were examined preoperatively and after surgery at 2 weeks, 3 months, 6 months, annually for 5 years, and at 10 years. Examinations in the morning and evening of the same day were done at 3 months, 1 year, 3 years, and 11 years in a subset of the patients to test for diurnal fluctuation of vision and refraction.

The primary outcome variables measured at each visit was the uncorrected and spectacle-corrected visual acuity and the refractive error with the pupil dilated and undilated. The corneal shape was measured with central keratometry and photokeratoscopy. Endothelial function was evaluated using specular microscopy. A slit-lamp microscope examination was made to check for complications from the incisions. Contrast sensitivity was tested in a subset of patients. Patient motivation and satisfaction were studied with psychometric questionnaires at baseline, 1 year, 5-6 years, and 10 years.

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Study Type : Interventional  (Clinical Trial)
Allocation: Randomized
Primary Purpose: Treatment
Study Start Date : April 1981
Actual Study Completion Date : October 1983

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Ages Eligible for Study:   21 Years and older   (Adult, Older Adult)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No
All men and women had 2 to 8 diopters of simple myopia and were correctable to 20/20 or better with glasses or contact lenses. All patients had the stability of their myopia documented by previous records. Patients were at least 21 years of age and lived in the metropolitan area of the study centers. Each patient agreed to have surgery on one eye and to wait 1 year for surgery on the other eye. Patients with systemic diseases that might affect corneal wound healing and patients with high corneal astigmatism were excluded from the study.
Additional Information:
Novak AF; Lindstrom RL; Williams PA; Everson M; Corneal pachymetry prior to radial keratotomy: a comparison of techniques., J Refract Surg 1985;1:151-153
Bourque LB; Cosand BB; Drews C; Waring GO; Lynn M; Cartwright C; Satisfaccion informada, fluctuacion de la vision y resplandor en pacientes al cabo de un ano tras la cirugia en el estudio de la evaluacion prospectiva de la queratotomia radial (EPQR)., Arch Ophthalmol 1986;2:57-64
Lynn MJ; Waring GO; Predictability and stability of radial keratotomy., J. Refract Surg 1987;3:193-196
Waring GO; Lynn MJ; McDonnell PJ; Resultados del estudio de evaluacion Prospectiva de la Queratotomia Radial (EPQR) 10 anos despues de la cirugia., Arch Ophthalmol (Edicion Espanola) 1995;6:99-110
Nizam A; Waring GO; Lynn MJ; Stability of refraction during 11 years in eyes with simple myopia., Invest Ophthalmol Vis Sci 1996;37:S1004

Layout table for additonal information Identifier: NCT00000129    
Other Study ID Numbers: NEI-28
First Posted: September 24, 1999    Key Record Dates
Last Update Posted: September 17, 2009
Last Verified: September 2009
Additional relevant MeSH terms:
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Refractive Errors
Eye Diseases