It is now >10 years since the remarkable discovery that photoreception in the mammalian retina occurs outside of rod and cone cells. In that time we have learnt a great deal about the melanopsin expressing retinal ganglion cells (mRGCs) that provide this non-rod non-cone photoreception, and about their extensive contribution to sub-conscious light responses. However, one idea that has persisted is that these mRGCs play little if any role in visual perception. Exciting new data challenge that view. Thus, we have recently described an extraordinarily extensive mRGC input to the primary visual pathway. This provides ~40% of neurones in the mouse visual thalamus with melanopsin signals, superimposed upon more conventional visual information. The discovery of this unexpected sensory input to the mammalian visual system raises several important questions: What does it contribute to vision? How is the melanopsin signal brought to the thalamus and how is it propagated/processed through higher visual centres? Does melanopsin help people with retinal degeneration (in which mRGCs long outlive rods and cones) to see? Could optimising melanopsin vision offer a new strategy for improving vision in these people? We propose addressing these questions by using state-of-the-art neurophysiological and anatomical techniques in mice. Our overarching objectives are Objective 1: What does melanopsin contribute to vision? Objective 2: How is melanopsin vision impacted by retinal degeneration?
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