Rpe Cells

As previously stated, postmitotic cells perform numerous metabolic functions throughout our lives, not only for themselves, but also for the photoreceptors. From about 20 years of age, the RPE cells show alteration as a result of their constant activity in the course of the years.

Each single RPE cell metabolically supports around 30 photoreceptors (Dryja et al., 1998).

Everyday, 10 to 15% of the acromeres of each rod are phagocyted by the RPE cells and replaced. The highest turnover of acromeres of retinal photoreceptors involves the parafoveal rods and the first signs of retinal aging appear in the macula. The subfoveal RPE maintains its function for the longest period, due to its high density of cones. A decrease in the functionality of the RPE occurs with aging, which manifests itself through various morphologic signs (Weiter et al., 1986). The signs of RPE aging consist of the reduction of the granules

Figure 67.5 The intercellular spaces of the outer layers of a retina harvested from a young man (19 years old). Numerous cellular processes and synaptic buttons can be seen. Finally, a presumed interplexiform cell may be identified (magnification 9600x). Reproduced by permission of the Canadian Ophthalmological Society.

Figure 67.5 The intercellular spaces of the outer layers of a retina harvested from a young man (19 years old). Numerous cellular processes and synaptic buttons can be seen. Finally, a presumed interplexiform cell may be identified (magnification 9600x). Reproduced by permission of the Canadian Ophthalmological Society.

Figure 67.6 Scanning electron photomicrograph showing the bulges of the outer nuclear layer appear tightly attached to one another, with only very narrow bridges of cellular matrix between them. The ganglion cells appear as large, spherical bodies, arranged in a fibrous network. Most of the cell bodies are smooth, but some of them were seen to have a villous surface. This retina was harvested from a young man (19 years old). Numerous synaptic bodies, cellular processes, and intercellular spaces may be observed (magnification 16000x). Reproduced by permission of Canadian Ophthalmological Society.

Figure 67.6 Scanning electron photomicrograph showing the bulges of the outer nuclear layer appear tightly attached to one another, with only very narrow bridges of cellular matrix between them. The ganglion cells appear as large, spherical bodies, arranged in a fibrous network. Most of the cell bodies are smooth, but some of them were seen to have a villous surface. This retina was harvested from a young man (19 years old). Numerous synaptic bodies, cellular processes, and intercellular spaces may be observed (magnification 16000x). Reproduced by permission of Canadian Ophthalmological Society.

of melanin (depigmentation) and the migration of the pigment granules to the basal portion of the cells, the loss of hexagonal shape of the foveal cells, the reduction on the cell density (atrophy, hyperplasia, hypertrophy, cellular migration), and the intracytoplasmatic accumulation of abnormal molecules due to incomplete degradation of the metabolic products in the form of intracytoplasmatic granules (lipofuscin, melanolipofuscin) (Young, l982). These granules are partially the result of a phagocytosis process of the acromeres of the rods and cones and their elimination by the phagosomes. Inside these latter, the gradual digestion of the discs of the acromeres, with the formation of residual bodies, occurs.

Many incompletely digested discs and some phagosomes are eliminated in the basal lamina of the Bruch's membrane. Large quantities of residual bodies are seen often in the eyes of individuals aged between 40 and 60, with a strong increase after the 80th year. The accumulation of this cellular detritus inevitably leads to the suffering of the RPE. These changes are more noted in the macula than in the equatorial and peripheral areas (Burns and Feney Burns, l980). Now we shall examine, in greater detail, the typical signs of RPE aging.

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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