AIM: To observe the pupil diameter in different environment on myopia control effect of orthokeratology.

METHODS: The optometry, pupil diameter and eye axial length were examined in 70 patients aged 8- to 13-year-old with low and moderate myopia, whom then were given night wear lenses, and we measured the length of eye axis and pupil diameter before wearing lenses, 6, 12 and 24mo after wearing. In two different light environment groups, each group took the average pupil diameter as the dividing and divided into two subgroups; the pupil diameter higher than the mean group(19 cases, 17 cases respectively), the pupil diameter lower than the mean group(16 case, 18 cases respectively). The paired t-test, independent sample t-test, repeated measures ANOVA and Pearson correlation analysis were adopted to analyze.

RESULTS: Whether in darkroom or exposed to natural light, the axial length of pupils whose diameter was lower than the mean diameter increased faster than that above the average diameter of pupils(P<0.01). The initial pupil diameter was significantly negatively correlated with the growth of the eye axis at the end of the 24-month follow-up(r=-0.4267,P<0.05; r=-0.4925,P<0.01).

CONCLUSION: The myopia controlling effect of orthokeratology under two different illumination conditions showed that the effect of myopia control in children with larger pupils is better than that in children with smaller pupils, which may be that the larger pupil makes the orthokeratology maintain stronger intervention on peripheral retina myopic defocus.