Abstract
Purpose :
This study aims to assess the stability of topography parameters performed after wearing orthokeratology lenses for year
Methods :
This is a retrospective study made on myopic patients seen at Université de Montréal Clinic, adapted for orthokeratology between January 2017 and December 2018, followed for at least 1 year, and having worn the same lens design during this period. Topographical data (Medmont) were extracted from tangential maps taken at baseline and after 1, 3, 6 and 12 months of wear. Following the map analysis method suggested by Marcotte-Collard et al, treatment zone diameter (TZD), mid-peripheral power (MPP), mid-peripheral power width (MPPW) were measured horizontally (180 deg) and vertically (90 deg) at each visit. These values were compared over time. Statistically, the repeated within-subject measures resulted in clusters of possibly correlated data. Models were fit that accounted for within-subject correlation. The predictors of main interest were Month and Quadrant. Also included were gender, ethnicity, age, flat keratometry (KF), Steep keratometry (KS), initial refraction (RX) and axial length.
Results :
Clinical population is composed of 99 participants (58% Female; 54% Asian), aged 11.75 +/- 2.15 showing an average refraction of -3.27 +/- 1.28D. Analysis of the results highlights all parameters remain stable during the first 6 months. However, at 12 months, TZD becomes smaller (-0.067+/-0.43mm) (p=0.004), MPP decreased by 0.89+/-2.82D (p<0.001), whilst its width (MPPW) remain stable at 0.99+/-0.25mm over time. The measures along the vertical meridian show higher convex power and larger width compared to the horizontal ones (p<0.001).
Conclusions :
This study demonstrates that topographic data can be compared over time. However, the convex power generated by the OK lens is significantly less at 12 months. Future work is needed to identify the causes of this loss of power. This could implicate that lenses must be changed more frequently in order to maintain their effectiveness.
This is a 2021 ARVO Annual Meeting abstract.