Influence of Baseline Myopic Refraction on Myopia Control in Youngsters Wearing Orthokeratology Lenses

Abstract

Objective: To evaluate the influence of baseline myopic refraction on controlling the development of myopia using orthokeratology in youngsters. Methods: This was a binocular self-control and case control study. A retrospective analysis of anisomyopic youngsters at Peking University Third Hospital was conducted from January 2009 to December 2017. Patients who wore orthokeratology lenses or spectacles in both eyes were recruited. Forty-nine youngsters (9-17 years old) who wore orthokeratology lenses were enrolled in the experimental group and 32 youngsters who wore spectacles were enrolled in the control group. The more myopic eye of each youngster was assigned to the experimental or control group Max and the less myopic eye of each youngster was assigned to experimental or control group Min. Refraction, corneal topography and axial length were measured at baseline and at the one-year visit. Data were analyzed with t test and Wilcoxon sign-rank test. Results: The mean spherical equivalence was -5.00±1.53 D and -3.06±1.60 D for the eyes in the experimental groups Max and Min, respectively (t=-20.593, P<0.001). There were no significant differences in corneal curvature, corneal astigmatism, corneal E value, corneal thickness or pupil diameter between the two subgroups. The mean baseline spherical equivalence was -5.05±1.43 D for the eyes in control group Max, and -2.81(-2.00, -4.38)D for eyes in control group Min (Z=-4.952, P<0.001). Axial length elongation was 0.03±0.14 mm in experimental group Max and 0.12±0.16 mm in experimental group Min at the one-year visit and the difference was statistically significant (t=-4.217, P<0.001). The median axial length elongation of eyes in control groups Max and Min was 0.49(0.07, 0.75)mm and 0.40(0.17, 0.50)mm (Z=-0.510, P=0.610), respectively. The mean interocular difference in axial length at the one-year visit (0.63±0.35 mm) was less than that at baseline (0.72±0.34 mm) (t=-4.217, P<0.001). In the control group, the mean interocular difference in axial length was 0.74±0.38 mm at baseline, and the median interocular difference in axial length was 0.83(0.38, 1.07)mm at the one-year visit but the difference was not statistically significant (Z=-0.510, P=0.610). Conclusions: A higher baseline myopic refraction can facilitate the effect of orthokeratology to slow axial growth in myopic youngsters. Key words: orthokeratology; myopia; inf luence factor; anisomyopia