Duplex retina
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A duplex retina is a retina consisting of both rod cells and cone cells,[1] which are the photoreceptor cells for two parallel but mostly separate visual systems. The rods enable the scotopic visual system, which is active in dim light. The cones enable the photopic visual system, which is active in bright light. While one is active, the other is generally inactive; either the rods are photobleached, or oversaturated, in bright light, or the cones are not sensitive enough to hyperpolarize, or instigate the phototransduction cascade, in dim light. However, at mesopic (twilight) conditions, both visual systems are active. In this region of overlap, both systems are active and combine to contribute to mesopic vision.[2]