Shedding Light On Cones

Daytime vision in vertebrates initiates with the absorption of light by cone photoreceptors (Rodieck, 1998), which generate signals for color discrimination (Sharpe et al., 1999). In humans, these cells are concentrated in a specialized part of the central retina called the fovea. This region of the eye operates over a wide range of intensities (Aguilar and Stiles, 1954) mediating high temporal (Green, 1970) and spatial visual resolution (Hart, 1987). The importance of the fovea to human vision is most clearly seen in the devastating disease, age-related macular degeneration (Bird, 2003). In line with these observations, cones in lower vertebrates (Normann and Perlman, 1979; Perry and McNaughton, 1991; Burkhardt, 1994) and primates (Schnapf et al., 1990) exhibit faster response kinetics and extended adaptation ranges when compared with rods,...