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Effects of orthokeratology with different back optic zone diameters on corneal biomechanics and myopia control: a
Ruisi Xie1, Yan Huo1, Xiaoqin Chen2,3
1School of Medicine, Nankai University, Tianjin, 300071, China.
Background:
To assess the long-term effects of orthokeratology (ortho-k) lenses with varying back optic zone diameters (BOZDs) on corneal biomechanical properties and explore their relationship with myopia control.
Methods:
This 1-year prospective, randomized, double-blind, self-controlled study enrolled 36 myopic children aged 9-12 years. Thirty subjects (60 eyes) completed the 1-year follow-up period. The subjects were randomly fitted with a 5-mm BOZD (5BOZD) lens in one eye and a 6-mm BOZD (6BOZD) lens in the fellow eye. Corneal biomechanics were measured using Corvis ST at baseline and at 1 day, 7 days, 1 month, 6 months, and 12 months after ortho-k wear. Axial length (AL) was measured at baseline, 6 months, and 12 months after ortho-k wear, and AL elongation (ΔAL) was calculated relative to baseline. Statistical analyses were performed to compare intergroup differences and examine the correlations between ΔAL and changes in biomechanical parameters.
Results:
ΔAL was significantly smaller in the 5BOZD groups compared to the 6BOZD groups at both 6 and 12 months (P < 0.05). The stiffness parameter at first applanation (SP-A1) significantly increased at 6 months in both groups (P < 0.05). At 12 months, the first applanation time (A1 time) and integrated radius significantly increased, while the first applanation velocity (A1 velocity) and stress-strain index (SSI) significantly decreased in both groups (P < 0.05). In the 6BOZD group, ΔAL showed a significant positive correlation with ΔA1 time at 6 and 12 months (r6m = 0.385, r12m = 0.424, P < 0.05).
Conclusions:
Long-term ortho-k therapy increased SP-A1, A1 time, integrated radius, and decreased A1 velocity, reflecting enhanced corneal resistance and elasticity. Compared to the 5BOZD lens, the traditional 6BOZD lens demonstrated relatively greater corneal elasticity, possibly reducing myopia control efficacy. A smaller BOZD may offset these corneal biomechanical changes and improve the management of myopia. Trial registration Chinese Clinical Trial Registry (ChiCTR2200061048).