Gas permeable (GP) versus non-GP lens wearers: accuracy of orthokeratology in myopia reduction

The primary objective of this study is to determine whether there are significant differences in visual and refractive outcomes between gas permeable (GP) and non-GP wearers following a 1-month period of overnight orthokeratology (OK).

The study included 14 subjects between the ages of 18 and 42 years. Group 1 consisted of six subjects wearing GP lenses for the correction of myopia for, at minimum, 1 year. Group 2 consisted of eight subjects wearing soft contact lenses or spectacles for the correction of myopia. All subjects were fit into the BE design in Boston XO material and lenses were worn for a period of 1 month. Unaided visual acuity using high (90%) and low (10%) contrast log MAR Bailey-Lovie vision charts, subjective refraction, corneal topography, and slit lamp evaluation were performed. Subjects were evaluated at day 1, 7, 14, 21, and 30.

One eye of each subject was considered for analysis; the eye with the better response was chosen based on post-OK measures. The mean post-OK spherical equivalent was 0.29 +/- 0.55 D in the GP group and 0.37 +/- 0.46 D in the non-GP group; the difference was statistically significant (p = 0.03). Baseline astigmatism decreased in the non-GP group after OK while there was no significant change in the GP group. The mean high contrast acuities were 0.06 +/- 0.12 in the GP group and 0.17 +/- 0.07 in the non-GP group (p = 0.05), whereas the low contrast acuities were 0.18 +/- 0.17 in the GP and 0.02 +/- 0.09 in the non-GP group (p = 0.01).

Although the non-GP group has higher post-OK visual acuity and spherical equivalent statistically, the GP group has attained an average unaided acuity of >20/20 and residual myopia <0.5 D. Clinically, this shows that OK can be a promising technique in GP wearers.