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pl. retinae [L.]
The innermost layer of the eye, which receives images transmitted through the lens and contains the receptors for vision, the rods and cones.
RETINA OF THE RIGHT EYE
retinal (-năl), adj.
The retina is a light-sensitive membrane on which light rays are focused. It extends from the entrance point of the optic nerve anteriorly to the margin of the pupil, completely lining the interior of the eye. It consists of three parts. The pars optica, the nervous or sensory portion, extends from the optic disk forward to the ora serrata, a wavy line immediately behind the ciliary process; the pars ciliaris lines the inner surface of the ciliary process; and the pars iridica forms the posterior surface of the iris. Slightly lateral to the posterior pole of the eye is a small, oval, yellowish spot, the macula lutea, in the center of which is a depression, the fovea centralis. This region contains only cones and is the region of the most acute vision. About 3.5 mm nasally from the fovea is the optic papilla (optic disk), where nerve fibers from the retina make their exit and form the optic nerve. This region is devoid of rods and cones and is insensitive to light; hence it is named the blind spot.
The layers of the retina, in the order light strikes them, are the optic nerve fiber layer, ganglion cell layer, inner synaptic layer, bipolar cell layer, outer synaptic layer, layer of rods and cones, and pigment epithelium.
RETINA Microscopic structure of optic disk area
The retina is normally red, reflecting blood flow, and is pale in anemia or ischemia.
The arteries are branches of a single central artery, which is a branch of the ophthalmic artery. The central artery enters at the center of the optic papilla and supplies the inner layers of the retina. The outer layers, including rods and cones, are nourished by capillaries of the choroid layer. The veins lack muscular coats. They parallel the arteries; blood leaves by a central vein that leads to the superior ophthalmic vein.