Soft Contact Lenses Can Induce Orthokeratology–Like Topographical Changes

Abstract

Abstract: : Purpose: Traditionally, orthokeratology has relied on rigid contact lenses to achieve the desired corneal reshaping effects. However, recent work has shown that soft lenses worn everted (inside out) can create similar changes to the corneal surface. The purpose of this study was to examine the topographical changes associated with the wearing of everted soft lenses of various designs and powers. Methods: One subject was used in this study. CIBA Focus Night and Day (lotrafilcon–A) 24% water lenses with base curves of 8.4mm, diameters of 13.8mm and powers of +6.00D, –0.25D, –6.00D and –10.00D were each everted and placed on one eye of the subject. Also evaluated were two custom soft lenses made in the Benz–G5X, (hioxifilcon–A) 59% water material with a base curve of 8.15mm, a diameter of 14.5mm and powers of –20.00D and –30.00D. The subject wore each of the everted lenses overnight for 6.5 hours and separately during the day for 6.5 hours. Each wearing period was separated by an appropriate period of non–lens wear to allow the cornea to return to baseline. All lens fits were evaluated with Fluoresoft 0.35% and photographed. The topographical changes between baseline and post–lens removal were analysed using the Medmont topographer. Results: Soft contact lenses worn everted resulted in corneal topographic changes generally consistent with traditional rigid lens orthokeratology; soft lenses worn without inversion resulted in very small topographic changes. Everted lenses of higher minus power showed more distinct Fluoresoft patterns and greater amounts of corneal topographic changes. For example, a –10D everted lens gave up to 2.50D of central flattening during daily wear, while a –20D everted lens gave up to 5.40D of central flattening. By comparison, the –10D lens produced 1.30D of flattening during overnight wear. The higher minus lenses were also found to induce a mid–peripheral ring of epithelial erosion. The Fluoresoft patterns of all everted lenses compare favourably with pressure profile patterns obtained mathematically using finite element analysis. Conclusions: It appears that everted soft contact lenses are capable of inducing significant changes in corneal topography, with daily wear resulting in greater topographic changes than overnight wear. Further work must be done to help understand these changes to develop a predictable and effective way of using soft contact lenses for corneal reshaping.

Keywords: contact lens • topography • cornea: epithelium