A single instillation of low-concentration atropine does not appear to produce measurable short-term changes in axial length, retinal thickness, or choroidal thickness in young adults, according to a randomized, double-masked study published in Eye and Vision. However, the study did identify a transient reduction in superficial retinal perfusion one hour after dosing, suggesting that atropine may have acute vascular effects even when structural parameters remain unchanged.
Low-dose atropine is now widely used in myopia management, particularly in children, but its mechanism of action remains incompletely understood. Although atropine was originally used for its cycloplegic effect, experimental evidence suggests that its anti-myopia activity may involve nonaccommodative pathways, including effects on retinal signalling, scleral remodeling, and possibly choroidal physiology.
To explore these acute responses, Barsha Lal and Lisa A. Ostrin, from the University of Houston College of Optometry, Texas, recruited 21 healthy adults aged 18–35 years. One participant withdrew after prolonged pupil dilation following 0.1% atropine, leaving 20 participants for analysis (10 males and 10 females). The final cohort had a mean age of 25.5 years and mean spherical equivalent refraction of −1.91 D.
Each participant attended five separate study sessions, receiving placebo, 0.01%, 0.025%, 0.05%, or 0.1% atropine in randomized order in the right eye. Sessions were spaced one to three weeks apart. At each visit, investigators measured axial length, retinal and choroidal thickness using spectral-domain OCT, and retinal and choroidal microvasculature using OCT angiography at baseline, one hour, and 24 hours after instillation.
The imaging protocol of the study included fovea-centered radial OCT scans to assess retinal and choroidal thickness in the central 1.0 mm and 1.0–3.0 mm annulus. OCTA was used to evaluate the superficial vascular complex, deep vascular complex, choriocapillaris, and foveal avascular zone.
Across all tested concentrations, atropine did not significantly alter axial length, retinal thickness, or choroidal thickness at either one hour or 24 hours. No concentration-dependent effect was detected. These findings contrast with some previous reports of short-term choroidal thickening after atropine, underlining the inconsistency of acute choroidal responses in the literature.
The only significant change was observed in OCTA-derived perfusion density. In the 1.0–2.5mm annulus, superficial vascular complex perfusion density decreased over time after atropine instillation, with post hoc analysis showing a significant reduction at one hour but not at 24 hours. Deep vascular complex perfusion, choriocapillaris perfusion, and foveal avascular zone area were unchanged.
The findings suggest that single-dose low-concentration atropine has little detectable acute effect on posterior segment structure in young adults, despite known dose-dependent effects on pupil size and accommodation reported previously by the same group. The transient OCTA signal may point to short-term vascular redistribution, but its clinical relevance remains uncertain.
Additionally, the study authors caution that the study assessed only single-dose effects, included a relatively small adult cohort, and did not examine children, the primary population for myopia control. Longer-term pediatric studies will be needed to determine whether repeated atropine exposure produces cumulative retinal or choroidal effects relevant to treatment response.
