Prospective Evaluation of Radial Keratotomy (PERK) Study

September 16, 2009 updated by: National Eye Institute (NEI)

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.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

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.

Study Type

Interventional

Phase

  • Phase 3

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

19 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Description

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.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Publications and helpful links

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General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

April 1, 1981

Study Completion (Actual)

October 1, 1983

Study Registration Dates

First Submitted

September 23, 1999

First Submitted That Met QC Criteria

September 23, 1999

First Posted (Estimate)

September 24, 1999

Study Record Updates

Last Update Posted (Estimate)

September 17, 2009

Last Update Submitted That Met QC Criteria

September 16, 2009

Last Verified

September 1, 2009

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

  • NEI-28

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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