The impact of amplitude of accommodation on controlling the development of myopia in orthokeratology

Abstract

To evaluate the impact of amplitude of accommodation on controlling the development of myopia in orthokeratology. Forty-nine children aged 7 to 14 years were enrolled in this prospective clinical study.Orthokeratology was performed to correct the refractive errors of these children after measurement of refraction, corneal topography, amplitude of accommodation and axial length. Axial length (AL) and amplitude of accommodation was measured after treatment. The average amplitude of accommodation was calculated and was used as the cutting point for dividing the cohort into "amplitude of accommodation above average" vs. "amplitude of accommodation below average". Data were analyzed by paired t-test, independent t-test, repeated measures-ANOVAs and Pearson correlation analysis. The AL before and after 1- year and 2-year treatment was (24.98 ± 0.75) mm, (25.13 ± 0.74) mm and (25.32 ± 0.78) mm, respectively. AL increased significantly throughout the observed 24-month period (F = 75.848, P < 0.001) . Amplitude of accommodation increased from (13.68 ± 2.65) D to (16.12 ± 2.41) D in 2 years (t = -6.461, P < 0.001) and amplitude of accommodation significantly affected axial growth (F = 7.395, P = 0.009) . The axial growth of subjects with below average amplitude of accommodation and those with above average amplitude of accommodation was (0.23 ± 0.25) and (0.44 ± 0.30) mm, indicating a statistically difference(t = -2.719, P = 0.009). AL change in subjects with below average amplitude of accommodation was 55.81% that of the subjects with above average amplitude of accommodation. Baseline amplitude of accommodation was positively correlated to axial growth at 24-month visit (r = 0.502, P < 0.001). Linear regression analysis was used between baseline amplitude of accommodation and 2-year axial growth: Axial growth = 0.055· Baseline amplitude of accommodation-0.409(F = 15.806, P < 0.001). The change of amplitude of accommodation for subjects with below average amplitude of accommodation and those with above average amplitude of accommodation after 2-year was (4.04 ± 2.16) D and (0.91 ± 2.15) D, indicating statistically difference (t = 5.084, P < 0.001). Myopic control effect would be more beneficial to lower amplitude of accommodation children than that to higher amplitude of accommodation children in orthokeratology. The enhancement of accommodation provides some basis for slowing myopia progression with orthokeratology.