An analysis of the changes in corneal shape and refractive error induced by accelerated orthokeratology

Abstract

The lack of predictability in orthokeratology has always been seen as one of the major drawbacks of the procedure. Being able to assess the likely degree of myopia reduction would be a valuable clinical tool in that those patients presenting for orthokeratology who would not be viable candidates could be advised against proceeding with a course of treatment. In this study the pre- and post-orthokeratology refraction, corneal eccentricity, keratometry, and apical corneal power changes were measured to see whether a correlation exists between the pre- and post-treatment corneal shape and refractive changes that could be used as a predictive tool. A good correlation was found between refractive change and corneal eccentricity change ( r 2 = 0.83), apical corneal power change and corneal eccentricity change ( r 2 = 0.84), and refractive change and apical corneal power change ( r 2 = 0.91). A poorer correlation was found between keratometry change and refractive, apical corneal power, and eccentricity change. The shape changes induced in the cornea by orthokeratology were also studied by topographical analysis. The final corneal shape is typically that of a central spherical zone (4.00–5.00 mm chord) surrounded by a mid-peripheral steep zone (5.00–7.50 mm chord) that tends to flatten in curvature as the periphery (8.00 mm chord) is approached.