NEI Clinical Studies
The information on this page is archived and provided for reference purposes only. It was current when it was produced, but may now be out-of-date. Persons having difficulty accessing this information may contact firstname.lastname@example.org for assistance. For reliable, current information on this and other topics, we recommend that you visit the National Eye Institute website index.
Berkeley Orthokeratology Study, The
- To evaluate the relative efficacy of orthokeratology, primarily by assessment of changes in central corneal thickness, astigmatism, visual acuity, endothelial cell density, and corneal curvature.
- To evaluate the relative safety of orthokeratology, primarily by assessment of changes in central corneal thickness, astigmatism, visual acuity, endothelial cell density, induced corneal edema, and epithelial staining.
- To assess the duration of any orthokeratology treatment effect.
- To study the mechanisms by which refractive error and visual acuity changes occur, in particular the contribution that comes from changes in corneal curvature and shape.
- To determine whether there were any predisposing ocular factors that could be used to predict which subjects will experience changes or complications.
In the early 1960s, a group of clinicians asserted that myopia could be reduced and possibly corrected by fitting specially designed contact lenses to induce corneal flattening and thereby reduce the refractive power of the eye. This technique, known as orthokeratology, required that the lenses be fitted and then changed progressively until vision becomes normal or nearly normal. Advocates of orthokeratology claimed that corneal changes could be induced in a predictable fashion, were often permanent, and occurred without causing any adverse effects to the cornea. Data on orthokeratology were generally limited, poorly documented, and did not address the issues of control or failure.
The Berkeley Orthokeratology Study was a single center randomized, concurrently controlled, masked clinical trial. Corneal and visual changes in an orthokeratology treatment group were monitored and compared with those observed in a control group whose members wore contact lenses fitted in a standard clinical manner. Visual and ocular characteristics were monitored for 1.5 years.
Eighty subjects were studied-40 in an orthokeratology group and 40 in a control group fitted with conventional hard contact lenses. The hard lenses chosen for this study were made of either polymethyl methacrylate (PMMA) or a PMMA-silicone combination (Polycon). All subjects were initially fitted with PMMA lenses.
The initial treatment and control lenses were selected according to protocol guidelines and then adjusted to achieve an "optimal fit" based on lens position, movement, and alignment as assessed by fluorescein study. At the outset, the treatment and control lenses differed in that the treatment lenses were on the average thicker and flatter and had a larger diameter.
Following the dispensing visit, subjects progressed through three study phases. In the adaption phase (Phase A), subjects were examined weekly until they were adapted to 12 to 14 hours of daily contact lens wear. The postadaptive phase (Phase B) consisted of monthly followup examinations for 1 year. The final phase (Phase C) consisted of a lens withdrawal segment and a postwearing segment.
Myopic volunteers, ages 20 to 35, who had not worn contact lenses were eligible to participate in the study if they were free of ocular disease, were in good physical health, and were not taking systemic medications that could have ocular side effects. In addition, eligibility was limited to persons with corneal curvature between 40.50 and 47.00 D (flatter keratometry reading), corrected visual acuity of 6/6 (20/20) or better in each eye, astigmatism less than 0.75 D, anisometropia less than 1 D, and myopia between 1 and 4 D.
Patient Recruitment Status
Completed. Patient recruitment began in January 1978 and ended in February 1979.
Current Status of Study
Data were available for 31 treated and 28 randomized control subjects who wore conventional rigid contact lenses. After an average of 444 days of contact lens wear, the treatment group showed an overall mean reduction in spherical equivalent refractive error of 1.01 D compared with 0.54 D in the control group (p = 0.02). Both groups had considerable variation in refractive error change. Corresponding mean improvements in unaided visual acuity were -0.27 and -0.20 log of the minimum angle of resolution. Corneal curvature decreased in both comparison groups, but the actual diopter value was about one-half that of the refractive change. The changes in these characteristics tended to occur during the first 132 days of wear, and additional aggressive lens therapy during the remaining 241 days of treatment produced little additional change. The refractive error fluctuated considerably during the periods of followup, and these fluctuations tended to be larger in those subjects who had shown greater changes in refractive error.
When the lenses were removed, ocular characteristics returned steadily toward baseline levels. Ninety-five days after discontinuing lens wear, the refractive error had returned to 75 and 69 percent of the way to baseline levels for the treatment and control groups, respectively. Visual acuity and corneal curvature showed similar rebound after 95 days.
With orthokeratology, it is possible to reduce myopia about 1 D; however, the change is not permanent. Results indicate that the level of vision during periods of non-lens wear would be unstable, making it difficult to predict what the quality of vision would be under a retainer lens wear program.
It appears that orthokeratology is safe for the types of patients who participated in this study, but it may require more patient monitoring than would be needed to achieve and maintain a physiologically acceptable fit with conventional hard contact lens prescriptions.
Orthokeratology produces modest reductions in myopia; however, the effect will not persist without continued lens wear and therefore is of limited clinical value in permanently reducing myopia.
Brand RJ, Polse KA, Schwalbe JS: The Berkeley Orthokeratology Study part 1: General conduct of the study. Am J Optometry and Physiological Optics 60: 175-186, 1983.
Polse KA, Brand RJ, Keener RJ, Schwalbe JS, Vastine DW: The Berkeley Orthokeratology Study, part III Safety. Am J Optometry and Physiological Optics 60: 321-328, 1983.
Polse KA, Brand RJ, Schwalbe JS, Vastine DW, Keener RJ: The Berkeley Orthokeratology Study, part II: Efficacy and duration. Am J Optometry and Physiological Optics 60: 187-198, 1983.
Polse KA, Brand RJ, Schwalbe JS, Vastine DW: Corneal Change Accompanying Orthokeratology: Plastic or elastic? Results of a randomized controlled clinical trial. Arch Ophthalmology 101: 1873-1878, 1983.
Polse KA, Brand RJ: Contact lens effects on ametropia: A current example of the clinical trial. Am J Optometry and Physiological Optics 58: 281-288, 1981.
Kenneth A. Polse, O.D.
School of Optometry
University of California, Berkeley
525 Minor Hall Annex
Berkeley, CA 94720
Telephone: (510) 642-7745
Donald F. Everett, M.A.
National Eye Institute
National Institutes of Health
Executive Plaza South, Suite 350
6120 Executive Boulevard MSC 7164
Bethesda, MD 20892-7164
Telephone: (301) 496-5983
Fax: (301) 402-0528
Last Updated: 10/21/99