Changes in Amacrine Cell Numbers and Morphology in Response To Induced Myopia and Hyperopia

Abstract

Myopia and hyperopia have been artificially induced in animal models by various manipulations of their early visual environment. Ametropias have been produced using lid suture1, changing illumination levels (dark-rearing2, constant light3, dim lighting4), intra-ocular injections5, treatment with defocussing lenses6, and the application of translucent occluders7. Abnormal ocular growth appears to be a major factor that causes ametropia. Myopic eyes are enlarged, while hyperopic eyes are smaller compared to control eyes. Changes in the sclera8, choroid9, and orbital bone10 surrounding the affected eyes also reflect abnormal growth mechanisms. Various studies11,12,13 suggest that the signal or signals which control eye growth may arise from within the retina itself. It has been suggested that retinal amacrine cells play a role in mediating ocular growth8. This study examines how dopaminergic and serotonergic amacrine cells are quantitatively and qualitatively affected by induced myopia and hyperopia.