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. Author manuscript; available in PMC: 2012 Mar 1.
Published in final edited form as: Prog Retin Eye Res. 2010 Nov 25;30(2):115–128. doi: 10.1016/j.preteyeres.2010.11.001

Figure 8. Retina and RPE visual cycles for cones.

Figure 8

After photolysis, all-trans RAL is reduced to all-trans ROL by RDH in cone outer segment. All-trans ROL can be either transported to the RPE cells and recycled to 11-cis RAL via the canonical visual cycle (refer to text and Figure 1), or transported to Müller cells where it is enzymatically converted to 11-cis ROL. 11-cis ROL is transferred back to cone inner segment, and then moves along the inner segment to the outer segment, where it is oxidized by an unidentified RDH to 11-cis RAL for pigment regeneration. The key enzymes, such as RDH and Isomerase II, in this pathway have not been identified. The role of the retinoid binding proteins CRALBP, CRBP, and IRBP in the retina visual cycle still needs to be determined.