Photoreceptors

Rods

Photoreceptors containing a single type of opsin; work best in dim light; responsible for peripheral vision; no color perception; ~100 million in the human eye

Cones

Photoreceptors with three types of opsins (S, M, L); work best in bright light; responsible for color vision; ~5 million in the human eye; concentrated in the fovea

Opsin

A photosensitive protein in photoreceptor cells; changes conformation when struck by a photon

Retinal (11-cis-retinal)

The chromophore (light-absorbing molecule) within opsin; when a photon hits it, it changes conformation, triggering the photoreceptor signal

Color Vision

Achieved by the activation of various combinations of the three cone types (short/blue, medium/green, long/red wavelength); color perception is context-dependent

S (Short) Cones/Blue Cones

Cone cells sensitive to short wavelengths (~400–450 nm, blue light)

M (Medium) Cones/Green Cones

Cone cells sensitive to medium wavelengths (~550 nm, green light)

L (Long) Cones/Red Cones

Cone cells sensitive to long wavelengths (~580–700 nm, red light)

Convergence (Retinal)

The processing of information in the retina before sending it to the brain; more than 100 million rods and cones feed into ~1 million optic nerve fibers; minimal in the central retina, high in the peripheral retina