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Effect of atropine on human multifocal electroretinogram responses to defocus Safal Khanal1, Philip RK Turnbull1, Nicholas Lee1, John R Phillips1,2 1. Myopia Laboratory, School of Optometry and Vision Science, The University of Auckland, New Zealand 2. Department of Optometry, Asia University, Taichung, Taiwan Purpose: Despite the global use of atropine in myopia control, the mechanism by which atropine acts to inhibit the progression of myopia is still unclear. This study investigates the effect of atropine on the human global flash mfERG under conditions of retinal defocus. Method: Global flash mfERG responses were recorded monocularly in the non-dominant eyes of nineteen healthy subjects (age: 23 ± 4 years) on a RETIScan system (Ronald Consult, Wiesbaden, Germany) using a 61-element hexagonal stimulus array scaled for eccentricity. Recordings were obtained under three randomised conditions of retinal defocus: 2.00D myopic defocus, 2.00D hyperopic defocus and no defocus using full-aperture ophthalmic lenses after correcting for testing distance. Each defocus condition was tested prior to the instillation of atropine, and then again 24 hours after instillation of 1 drop 0.1% atropine. Signals reflecting activity from outer and inner retinal layers – direct (DC) and induced (IC) components respectively – were analysed separately. The mfERG responses were pooled within central (0° to 6°) and peripheral (6° to 24°) retinal zones, and compared across the experimental conditions, relative to the baseline (i.e. no defocus, no atropine condition). Results: Within the central zone, atropine had no effect on the amplitudes and implicit times of the DC or IC responses to defocus. Within the peripheral zone, atropine had a significant main effect of increasing DC amplitudes (F1,18= 7.821, p= .012) and implicit times (F1,18= 15.406, p= .001) in response to defocus. For the IC responses, there was a significant interaction effect of atropine and defocus (F2,36= 6.050, p= .011) with greater post-atropine amplitudes under myopic defocus (mean difference= 15.52%, 95% CI= 5.627 to 25.421, p= .004). Atropine also had a significant main effect of increasing IC implicit times (F1,18= 9.722, p = .006). Conclusion: Our results imply that atropine acts in the peripheral retina to enhance mfERG responses in areas of the retina experiencing myopic defocus. These findings suggest that atropine may potentiate the effects of myopic defocus in inhibiting axial eye growth and myopia. |
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