Sclera, choroid, and retina.

This section of the wall of an eye shows the dense connective tissue of the sclera (S) and the loose, vascular connective tissue of the choroid (C). Melanocytes are prominent in the choroid, especially in its outer region, the suprachoroidal lamina (SCL). The choroid's inner region, the choroidocapillary lamina (CCL), has a rich microvasculature which helps provide O2 and nutrients to the adjacent retina. Between the choroid and the retina is a thin layer of extracellular material known as Bruch's layer (B). The outer layer of the retina is the pigmented layer (P) of cuboidal epithelium containing melanin. Adjacent to this are the packed photoreceptor components of the rods and cones (R&C), the cell bodies of which make up the outer nuclear layer (ONL). Junctional complexes between these cells are aligned and can be seen as a thin line called the outer limiting layer (OLL). Axons of the rods and cones extend into the outer plexiform layer (OPL) forming synapses there with dendrites of the neurons in the inner nuclear layer (INL). These neurons send axons into the inner plexiform layer (IPL), where they synapse with dendrites of cells in the ganglionic layer (GL). Axons from these cells fill most of the nerve fiber layer (NFL) which is separated by the inner limiting layer (ILL) from the gelatin-like

connective tissue of the vitreous body (VB). X200. H&E.

Retina

The retina, the inner layer of the eye, is derived from the embryonic optic cup. Like the optic cup, the retina consists of two major layers. The inner one, the neural retina, contains the neurons and photoreceptors. This layer's visual region extends anterior only as far as the ora serrata, but it continues as a cuboidal epithelium lining the surface of the ciliary body and posterior iris. The outer pigmented layer is an epithelium resting on Bruch's membrane just inside the choroid. This pigmented, cuboidal epithelium also lines the ciliary body and posterior iris, contributing to the double epithelium described with those structures.

The pigmented epithelium consists of low columnar cells with basal nuclei. The cells have well-developed junctional complexes, gap junctions, and numerous invaginations of the basal membranes associated with mitochondria. The apical ends of the cells extend processes and sheath-like projections that surround the tips of the photoreceptors. Melanin granules are numerous in the extensions and apical cytoplasm. This cellular region also contains numerous phagocytic vacuoles and secondary lysosomes, peroxisomes, and abundant smooth ER, with specialized regions in these cells for isomerization of all-trans -retinal (derived from vitamin A) and its transport to the photoreceptors. The diverse functions of the cells in the retinal pigmented epithelium include the following:

- serve as an important part of the blood-retina barrier,

- absorb light passing through the retina to prevent its reflection,

- hagocytose shed components from the adjacent rods and cones, remove free radicals, and -

- isomerize and regenerate the retinoids used as chromophores by the rods and cones.

Дата добавления: 2015-10-30