Low-concentration atropine for management of myopia progression: does iris colour matter?

BACKGROUND: To investigate interactions between iris colour and low-concentration atropine on outcomes relevant to clinical myopia management METHODS: A post-hoc, exploratory meta-analysis of three randomised clinical trials investigating atropine 0.01% or 0.05% eye drops vs placebo: the Western Australian Atropine Treatment of Myopia study, the Myopia Treatment Study and the Myopia Outcome Study of Atropine in Children. Iris colour was graded as brown or not brown (including blue/green/hazel). Change in accommodative amplitude, pupil diameter, spherical equivalent refraction (SER) and axial length were assessed using linear mixed models. RESULTS: In participants (baseline ages 5-16 years) using atropine 0.01% (n = 396), pupil diameter change did not differ by iris colour (p ≥ 0.15), while accommodative amplitude decreased more in not brown vs brown iris colour groups at month 12 (adjusted difference = -1.07D, 95% CI: -2.02, -0.12, p = 0.03), but not at month 24 (p = 0.76). Change in pupil and accommodative outcomes with 0.05% atropine (n = 66) did not differ by iris colour (p ≥ 0.10). Among not brown iris colour participants, myopia progression was lower in the atropine 0.01% vs placebo group at 24 months (SER: +0.17D, 95% CI: 0.07, 0.26, p < 0.001; axial length: -0.09 mm, 95% CI: -0.12, -0.05, p < 0.001), but not among brown iris colour participants (SER: -0.08D, 95% CI: -0.20, 0.05; axial length: +0.03 mm, 95% CI: -0.02, 0.07). CONCLUSION: Change in pupil diameter and accommodative amplitude with low-concentration atropine largely did not differ between iris colour groups. Among participants using 0.01% atropine eye drops, there was less 24-month myopia progression compared to placebo in participants with blue/green irides, but not with brown irides.