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The central retina of humans, apes and monkeys is uniquely characterized amongst mammals by the presence of the macula, a distinct and specialized area 6 mm in diameter (≈22 degrees of visual angle) centered on the fovea (Curcio et al., 2000). The fovea which measures just 0.8 mm and contains the highest photoreceptor and RPE densities in the retina, enables the high visual acuities achieved by primates. A defining characteristic of the macula includes the presence of the xanthophyll pigments, lutein and zeaxanthin, which give the macula its distinctive yellow color (Snodderly et al., 1984). Within the macula, rods outnumber cones by 9:1, lower than the 20:1 rod to cone ratio found for the retina as a whole (Curcio et al., 2000). Therefore, while the macula is cone enriched compared with the peripheral retina, rods are the predominant photoreceptor. In primates, the macula is surrounded by the “rod ring”, an area with a radius of approximately 10 to 25 degrees, which contains the highest rod density within the retina (Curcio et al., 1990; Packer et al., 1989; Wikler et al., 1990). For the purposes of the present paper, the central retina is taken to be the area covering 40 degrees of visual angle which encompasses the macula and much of the surrounding rod ring. With increasing age, changes in retinal morphology include an overall thinning of the retina, accumulation of lipofuscin within the retinal pigment epithelium, thickening of Bruch’s membrane, accumulation of basal deposits on and within Bruch’s membrane, and accumulation of drusen, the extracellular deposits below the retinal pigment epithelium (Bonilha 2008). The number of photoreceptors within the central and peripheral retina are differentially affected by age. Within the central retina, rod density decreases by 30% between 20 and 90 years of age, while cone density remains constant at the fovea and across

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Electroretinogram Assessment of Dark Adaptation and Rod Phototransduction from the Central Retina of Japanese Macaques with Dominantly Inherited Drusen