Response of accommodation and vergence systems to low dose atropine

Few studies have comprehensively investigated the effect of low dose atropine on the binocular vision system beyond accommodative amplitude. This study examined the effect of 0.05% atropine eye drops on a range of accommodation and vergence parameters across a 10-day period.

Twenty myopic, adult participants (mean age [SD] 22.3 [1.0] years, mean spherical equivalent refraction [SD] -1.9 [1.0] D) were randomised to receive either atropine (0.05% atropine sulphate, n = 10) or control (0.9% sodium chloride, n = 10) eye drops for nightly use for nine consecutive nights. Accommodative posture, monocular and binocular accommodative amplitude (AA), positive and negative relative accommodation (PRA/NRA), binocular accommodative facility (BAF), distance and near heterophoria, positive and negative fusional vergences (PFV/NFV), near point of convergence (NPC) and gradient accommodative convergence to accommodation ratios (AC/A) were measured at baseline, day-3 and day-10.

By day-10, accommodative lag had increased significantly and AA, PRA and BAF had all decreased significantly in the atropine group, while there were no significant changes in any of the control group measurements. Near heterophoria shifted significantly towards esophoria and the NFV break and recovery points were decreased significantly in the atropine group by day-10. Additionally, NPC reduced by a clinically significant amount (that bordered on statistical significance), with no changes found in the control group. There was no significant change in distance heterophoria, AC/A, NRA or PFV (all p > 0.05) at day-3 or day-10 in either treatment group.

Atropine (0.05%) use disrupted accommodation significantly over 10 days and increased convergence at near. While near heterophoria shifted towards esophoria, participants' ability to counteract this was also diminished by a reduction in NFV. This suggests that the near heterophoria and fusional reserves of children using 0.05% atropine for myopia control should be monitored closely.