Effects of hemiretinal form deprivation on central refractive development and posterior eye shape in chicks

We determined effects of hemiretinal form deprivation (i.e., form-depriving half of the retina) on central refractive development and posterior eye shape in chicks. Seventy-seven White Leghorn chicks were randomly assigned to receive superior (SRD, "Superior Retinal Deprivation" or inferior visual field deprivation, same principle applies for the following abbreviations, n=17), inferior (IRD, n=14), temporal (TRD, n=23) or nasal hemiretinal (NRD, n=23) form deprivation monocularly from day 5 to day 26. Central refractive errors, expressed as interocular difference in spherical equivalent (M), J0 and J45 astigmatic components, were measured using Hartinger refractometer at the beginning and weekly after treatment for 3weeks. At the end of the treatment period, eyes of a subset of birds were enucleated and eye shape profile was photographed along four different meridians. These digital images were later processed to extract axial length (AL), equatorial diameter (ED), and AL/ED. For comparison purposes, the eye shape profile was also acquired from a separate group of birds reared with monocular full-retinal form deprivation (FRD, n=10). The four hemiretinal form deprivations altered central ametropia and posterior eye shape to different degrees. The biggest contrast in M was found between SRD and IRD groups (mean±SE after 3weeks: SRD=-4.14±0.71 D vs. IRD=+1.24±0.36 D; p<0.05), whereas subtle differences in J0 and J45 components were found across the four treatment groups (both p⩽0.03). SRD group also showed significantly higher AL/ED ratio compared to IRD and NRD groups (0.76±0.05 vs. 0.74±0.07 and 0.75±0.04; both p⩽0.03). Furthermore, M was significantly correlated with AL/ED ratio in the treated eyes of hemiretinal treated chicks (r=-0.55, p<0.001). Our results suggest that mechanism regulating central ametropia can be influenced by selectively interrupting the visual experience at different parts of visual field.