retina

(ret’in-ah) [1,.. The innermost tunic and perceptive structure of the eye, formed by the expansion of the optic nerve, and covering the back part of the eye as far as the ora serrata. It consists of ten layers, named, from within outward, as follows: (1) The membrana limitans intern a; (2) the nerve-fiber layer; (3) the layer of ganglion-cells; (4) the inner molecular, or plexiform, layer; (5s) the inner nuclear layer; (6) the outer molecular, or plexiform, layer; (7) the outer nuclear layer; (8) the membrana limitans extern a; (9) the layer of rods and cones (called also Jacob’s membrane and bacillary layer); and (10) the pigmentary layer. This last layer consists of pigmented epithelial cells, and is continued forward over the inner surface of the ciliary body, and is known as the pars cilia’ris ve’ine. The various layers are connected transversely by fibers of connective ti ue (sustentacular fibers of Muller). The layer of rods and cones forms the percipient clement of the retina and is connected by nerve-fibers with the nerve fiber layer, which join to form the optic nerve. In the center of the posterior part of the retina is the macula lu’tea, the most sensitive portion of the retina; and in the center of the macula lutea is a depre ion, the fot’ea centra’lis, from which the rods are absent. About, inch inside the fovea is the point of entrance of the optic nerve and its central artery (central artery of the retina). At this point the retina is incomplete and forms the blind spot. coarctate r., a funncl-shaped condition of the retina caused by a fluid exudation between the retina and the choroid. leopard r., a retina of a variegated or mottled appearance, due to retinitis pigmentosa. lower r., the lower half of the retina. nasal r., the nasal half of the retina. shot-silk r., an opalescent effect, as of changeable silk, sometimes seen in the retinas of young persons. temporal r., the outer half of the retina. tigroid r., the striped or spotted retina of retinitis pigmentosa. upper r., the upper half of the retina.