Retina

The retina represents the innermost layer of the eye

The retina, derived from the inner and outer layers of the optic cup, is the innermost of the three concentric layers of the eye (see Fig. 23.1c). It consists of two basic layers:

• Neural retina or retina properthe inner layer that contains the photoreceptors

• RPE, the outer layer that rests on and is firmly attached to the choriocapillary layer of the choroid

A potential space exists between the two layers of the retina. The two layers may be separated mechanically in the preparation of histologic specimens. Separation of the layers, "retinal detachment" (see Box 23.2), also occurs in the living state as a result of eye disease or trauma.

In the neural retina, two regions or portions that differ in function are recognized:

• The nonphotosensitive region {nonvisual part), located anterior to the ora serrata, which lines the inner aspect of the ciliary body and the posterior surface of the iris (this portion of the retina is described in the sections on the iris and ciliary body)

• The photosensitive region (optic pari:), which lines the inner surface of the eye posterior to the ora serrata except where it is pierced by the optic nerve (see Fig. 23.1)

The site where the optic nerve joins the retina is called the optic papilla or disc. Because the optic papilla is devoid of photoreceptors, it is a blind spot in the visual field. The fovea centralis is a shallow depression located about 2.5 mm lateral to the optic disc. It is the area of greatest visual acuity. The visual axis of the eye passes through the fovea. A yellow-pigmented zone called the macula lutea surrounds the fovea. In relative terms, the fovea is the re gion of the retina that contains the highest concentration and most precisely ordered arrangement of the visual elements.

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