Orthokeratology in low myopia. Part 1: efficacy and predictability

Abstract

Aims Modern orthokeratology (ortho-k) using reverse geometry lens designs is being widely used for myopia reduction world-wide although there has been no well-controlled clinical trial of this procedure. This paper reports on the efficacy and predictability of an ortho-k procedure using the OK-74 lens design (now known as OK-704). Methods. We carried out a 100-day, controlled, randomised clinical trial in which 14 subjects underwent ortho-k and a further 14 were fitted with aligned rigid contact lenses. Results The mean reduction in myopia was 1.50 (SD 0.45) D in the ortho-k group and 0.01 (SD 0.20) D in the control group. Unaided vision improved by −0.64 (SD 0.22) logMAR units in the ortho-k group, compared with −0.09 (SD 0.11) units in the control group. Variables which correlated with refractive change were corneal thickness, p-value of the nasal semi-meridian and the difference between central and peripheral corneal powers. A multiple factors model can account for 72% of the refractive change. Conclusions Ortho-k using the OK-74 lens design achieved an average myopia reduction of 1.50 D. The model developed can provide an estimate of the refractive change likely to occur in ortho-k, a matter of importance to both clinician and patient.