L-opsin expression in chickens is similarly reduced with diffusers and negative lenses

Previous studies have shown that the expression of L- and M-opsins was reduced in chicken retina when eyes were covered with diffusers. The purpose of the current study was to find out whether this is a result of altered spatial processing during development of deprivation myopia or merely a consequence of light attenuation by the diffusers. Therefore, retinal luminances were matched by neutral density filters in fellow eyes that served as controls for diffuser-treated eyes. Furthermore, the effects of negative lenses on opsins expression were studied. Chickens wore diffusers or -7D lenses for a period of 7 days and refractive state and ocular biometry were measured at the beginning and at the end of the experiment. Retinal tissue was extracted from both eyes to quantify L-, M- and S-opsins expression by qRT-PCR. It was found that L-opsin expression was significantly lower in eyes wearing diffusers, compared to fellow eyes covered with neutral density filters. Interestingly, L-opsin was also reduced in eyes wearing negative lenses. In summary, this study shows that L-opsin expression is reduced due to the loss of high spatial frequencies and general contrast reduction in the retinal image, rather than by a decline in retinal luminance. Moreover, the fact that L-opsin was similarly reduced in eyes treated with negative lenses and diffusers suggests the existence of a common pathway for emmetropization, but it could also be just a consequence of reduced high spatial frequencies and lower contrast.