Association between pupil size and response to atropine therapy in the Atropine Treatment of Myopia study (ATOM2)

To determine if pupil size at baseline, on treatment, or change in pupil size while on atropine was associated with myopia progression.

This study utilized data from the ATOM2 study, a prospective, randomized, double-masked trial. 400 children were randomized to receive atropine 0.5%, 0.1%, or 0.01% daily in both eyes in a 2:2:1 ratio. Demographic data, as well as pupil size (PS) under photopic (300 lx) and mesopic (4 lx) conditions, axial length (AL), and spherical equivalent (SE) data at baseline and on follow-up, were collected.

At baseline, the mean photopic and mesopic pupil size was 3.96+/-0.63 mm and 4.48+/-0.66 mm, respectively. Pupils on higher doses were more dilated, with eyes with smaller PS at baseline having smaller PS on treatment. Multivariate analysis suggested that changes in axial length (AL) and spherical equivalent (SE) were strongly associated with age and change in PS, while PS on treatment was also associated with change in AL after controlling for sex, race and atropine dose. Receiver operating characteristic analysis, however, suggested that change in PS was a poor predictor of treatment response (area under curve: 0.53-0.69), with sensitivity being better than specificity. So while a larger change in PS (e.g. ≥2.5 mm in 6.0-8.9year old children, or ≥2 mm in older children) was more likely to be associated with a better result; having a smaller PS change did not necessarily suggest a poor result.

A larger change in pupil size on treatment was associated with a better treatment response.