Objective To evaluate the long-term effects of orthokeratology (ortho-k) lenses with different back optical zone diameters (BOZD) on the quality of vision in myopic children.

Methods We conducted an exploratory analysis based on a prospective, randomized, double-blind clinical trial, focusing on the parameters related to visual quality. A total of 66 myopic children aged 8 to 12 years were enrolled and randomly assigned to either a 6-mm BOZD ortho-k lens group (the 6 mm group) or a 5-mm BOZD ortho-k lens group (the 5 mm group). The participants were followed up at baseline, and at 1 day, 1 week, and 1, 3, 6, 9, and 12 months after lens wearing. Visual quality measurements included uncorrected visual acuity (VA), best corrected VA, contrast sensitivity (CS), high-order aberrations (HOA), modulation transfer function (MTF), Strayer ratio (SR), and visual quality questionnaire.

Results A total of 63 children (33 children in the 6 mm group and 30 children in the 5 mm group) completed the study. There were no significant differences in baseline data between the two groups (P > 0.05). There were no significant differences in subjective uncorrected VA or best corrected VA between the two groups at any follow-up visit (P > 0.05). After wearing the lenses for 3 months, the CS at high spatial frequency (18 cpd) in the 5 mm group was lower than that in the 6 mm group (P = 0.015). However, at 12 months, no significant differences in the CS were found between the two groups (P > 0.05). The ocular and corneal total HOA, spherical aberration, and coma aberration in both groups increased after wearing the lenses, and the HOA in the 5 mm group was higher than that in the 6 mm group (all P< 0.05). After wearing the lenses for 3 months, the MTF and SR values in the 5 mm group were lower than those in the 6 mm group (P < 0.05). At 12 months, there was no significant difference between the two groups (P > 0.05). The vision-quality-related questionnaire scores showed no significant differences between the two groups (P > 0.05).

Conclusion In myopic children, wearing ortho-k lenses with different BOZD results in improved subjective satisfaction, with no difference in subjective visual quality. However, objective visual quality declined in both groups, with a greater impact observed in the 5 mm group.