Anatomy

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9

serves to nourish the outer portion of the underlying retina

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The Lens

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The lens is a biconvex, avascular, colorless, and almost completely transparent structure, about 4 mm thick and 9 mm in diameter.

It is suspended behind the iris by the zonule, which connects it with the ciliary body

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lens gradually becomes larger and less elastic throughout life.

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The lens consists of about 65% water, about 35% protein (the highest protein content of any tissue of the body). Potassium is more concentrated in the lens than in most tissues.

There are no pain fibers, blood vessels, or nerves in the lens

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The Retina

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The retina is a thin, semitransparent, multilayered sheet of neural tissue that lines the inner aspect of the posterior two-thirds of the wall of the globe.

It extends almost as far anteriorly as the ciliary body, ending at that point in a ragged edge, the ora serrata .

The outer surface of the sensory retina is apposed to the retinal pigment epithelium and thus related to Bruch's membrane, the choroid, and the sclera.

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In most areas, the retina and retinal pigment epithelium are easily separated to form the subretinal space, such as occurs in retinal detachment. But at the optic disk and the ora serrata, the retina and retinal pigment epithelium are firmly bound together, thus limiting the spread of subretinal fluid in retinal detachment.

This contrasts with the potential suprachoroidal space between the choroid and sclera, which extends to the scleral spur. Choroidal detachments thus extend beyond the ora serrata, under the pars plana and pars plicata.

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The layers of the retina, starting from its inner aspect, are as follows: (1) internal limiting membrane; (2) nerve fiber layer, containing the ganglion cell axons passing to the optic nerve; (3) ganglion cell layer; (4) inner plexiform layer, containing the connections of the ganglion cells with the amacrine and bipolar cells; (5) inner nuclear layer of bipolar, amacrine, and horizontal cell bodies; (6) outer plexiform layer, containing the connections of the bipolar and horizontal cells with the photoreceptors; (7) outer nuclear layer of photoreceptor cell nuclei; (8) external limiting membrane; (9) photoreceptor layer of rod and cone inner and outer segments; and (10) retinal pigment epithelium .