Effect of atropine on the response of human choroid to retinal image defocus in myopia

Abstract

Purpose: Both atropine and retinal defocus modify myopia progression in humans. The choroid has been implicated in eye growth and myopia development, particularly in animals. This study investigated the interaction of atropine and imposed retinal defocus on subfoveal choroidal thickness (SFCT) in humans. Methods: Following a preliminary study in 10 young adults, 20 Taiwanese children (aged 6 to 14 years) with myopia (-0.75D to -4.00D) entered the main study. During distance viewing, SFCT was monitored by Optical Coherence Tomography (OCT) in both eyes while 2.00D of hyperopic and myopic retinal defocus (randomly ordered) was imposed in the experimental eye for 60 minutes, with the contralateral Control eye fully corrected for distance. These protocols were repeated before 0.3% atropine treatment and after 1 week, 3 and 6 months of treatment to both eyes. Results: In the preliminary study, hyperopic defocus caused SFCT to thin (maximum at 40-mins) by 10±2μm; p=0.004). Twenty-two hours after instilling 0.5% atropine, baseline SFCT had not changed (p=0.16) and hyperopic defocus failed to thin the choroid (Maximum change in SFCT = +2±2μm, p=0.36). In the main study, before atropine, 60 minutes of myopic and hyperopic defocus induced thicker and thinner choroids respectively (Myopic: 12±2 μm, p<0.01, and Hyperopic: 12±2 μm, p<0.01), whereas SFCT in Control eyes did not change (p>0.20). After 1 week of 0.3% atropine, baseline SFCT (without defocus) in both eyes had increased by ~20μm, p<0.01, and 60 minutes of hyperopic defocus failed to cause choroidal thinning (p>0.05), although myopic defocus still caused a further increase in SFCT. This additive effect remained after 3 and 6 months of atropine treatment. Conclusions: The normal reduction in SFCT in response to hyperopic retinal defocus is inhibited by atropine, while the normal increase in SFCT with myopic defocus is unaffected. This may imply that choroidal thinning and thickening are mediated by different mechanisms. These changes are superimposed on an increased baseline SFCT caused by atropine. The additive effect of myopic defocus and atropine on choroidal thickening suggests that combining optical and pharmaceutical therapies into dual therapies is likely to provide more effective myopia control than either therapy alone.