TAILIEUCHUNG - Chapter 029. Disorders of the Eye

The cones function under daylight (photopic) conditions. The cone system is specialized for color perception and high spatial resolution. The majority of cones are located within the macula, the portion of the retina serving the central 10° of vision. In the middle of the macula a small pit termed the fovea, packed exclusively with cones, provides best visual acuity. Photoreceptors hyperpolarize in response to light, activating bipolar, amacrine, and horizontal cells in the inner nuclear layer. . | Chapter 029. Disorders of the Eye The cones function under daylight photopic conditions. The cone system is specialized for color perception and high spatial resolution. The majority of cones are located within the macula the portion of the retina serving the central 10 of vision. In the middle of the macula a small pit termed the fovea packed exclusively with cones provides best visual acuity. Photoreceptors hyperpolarize in response to light activating bipolar amacrine and horizontal cells in the inner nuclear layer. After processing of photoreceptor responses by this complex retinal circuit the flow of sensory information ultimately converges upon a final common pathway the ganglion cells. These cells translate the visual image impinging upon the retina into a continuously varying barrage of action potentials that propagates along the primary optic pathway to visual centers within the brain. There are a million ganglion cells in each retina and hence a million fibers in each optic nerve. Ganglion cell axons sweep along the inner surface of the retina in the nerve fiber layer exit the eye at the optic disc and travel through the optic nerve optic chiasm and optic tract to reach targets in the brain. The majority of fibers synapse upon cells in the lateral geniculate body a thalamic relay station. Cells in the lateral geniculate body project in turn to the primary visual cortex. This massive afferent retinogeniculocortical sensory pathway provides the neural substrate for visual perception. Although the lateral geniculate body is the main target of the retina separate classes of ganglion cells project to other subcortical visual nuclei involved in different functions. Ganglion cells that mediate pupillary constriction and circadian rhythms are light sensitive owing to a novel visual pigment melanopsin. Pupil responses are mediated by input to the pretectal olivary nuclei in the midbrain. The pretectal nuclei send their output to the Edinger-Westphal nuclei which .

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