The Essential Role of Retinoids as Ligands for Visual Pigment Formation in and Survival of Cone Photoreceptors

Authored by: Peter H. Tang , Rosalie K. Crouch

CRC Handbook of Organic Photochemistry and Photobiology

Print publication date:  March  2012
Online publication date:  March  2012

Print ISBN: 9781439899335
eBook ISBN: 9781466561250
Adobe ISBN:


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The retina is the crucial component of the eye that is responsible for converting environmental light into neuronal signals by a process called phototransduction. Photoreceptor cells are specialized photo-transducing neurons within the retina and are divided into two families: rods and cones. Rods mediate low-light monochromatic vision, and cones mediate color and bright-light vision. Their patterns of distribution differ within the human retina; rods are found throughout, whereas cones are localized mainly within the fovea to mediate central vision. Although both rods and cones contribute to sight, humans, like other diurnal animals, exhibit a far greater dependence on cones for daily activity. Intrinsic to the phototransduction pathway are vitamin A derivatives called retinoids that are used to generate the chromophore for visual pigment formation within rods and cones [1,2]. After light excitation, the ligand/chromophore is recycled through a multistep enzymatic process called the visual cycle, with the retinal pigment epithelium 65 kDa protein (RPE65) playing an essential role as the isomerohydrolase. In the following chapter, we will explore the contributions of retinoids and RPE65 to cone function, as well as the pathogenesis of cone loss associated with RPE65 dysfunction.

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