Investigation of the cues underlying myopia and their association with retinal neuronal nitric oxide synthase in the guinea pig eye

Background and Aims. Myopia occurs when distant objects are imaged in front of the retina and thus appear blurred. It typically develops if the growth of the eye is too great for its decreasing optical power during emmetropisation. High myopia is associated with serious ocular disease and is recognised as a leading cause of vision impairment globally. The cause(s) of the extraordinary increases in the prevalence of myopia, particularly in East Asia, are unknown. Animal models have demonstrated that myopia can be induced by depriving the eye of visual detail (form deprivation, FD) and when retinal defocus is imposed with lenses. Exposure to high light levels or outdoor activity can slow or delay the onset of myopia, suggesting retinal light signals may be involved. An important light signal present in the retina is nitric oxide (NO). NO is critically involved in light adaptation and its related enzyme, neuronal NO synthase (nNOS), is an important mediator of the choroidal response to myopia recovery in the chick. In the mammalian retina, the expression of nNOS in the guinea pig eye is changed in opposite directions depending on the direction of ocular growth. The guinea pig provides a useful mammalian model of myopia, due to a rapid response to both FD and lensimposed defocus. In this thesis, these paradigms were extended to further investigate the association between retinal nNOS and features underlying myopia.