Aging Of The Bruchs Membrane

The human Bruch's membrane ages in a manner similar to the inner tunic of the arteries and other connective tissues, in which the plasmatic lipoproteins represent the known source of extracellular cholesterol. Morphologic and biochemical studies have shown that with aging the Bruch's membrane undergoes profound changes, such as the thickening and progressive accumulation of deposits in the internal layers. The changes to the Bruch's membrane progressively reduce the efflux of fluids from the retina to the choroids and the metabolic exchange between the choriocapillaries and the RPE cells. Moore and Clover (2001) have shown that there is an age-related reduction in the permeability (hydraulic conductivity) of the Bruch's membrane in the retinal periphery and the macula. Furthermore, it has been shown that the presence of lipid deposits plays a statistically important role in the reduction of permeability of the Bruch's membrane. Lipids are one of the components of the Bruch's membrane. The other components are collagen, adhesion molecules, lipoproteins, and advanced glycosyl-ation end products (the last of which may inhibit the activity of the lysosomal enzymes). The effect of aging on the passage of metabolites across the Bruch's membrane needs to be better ascertained. However, two groups of studies have demonstrated that the flux of macromolecules reduces with age. The first group, using fluorangiography, showed that in the ocular fundus (Figures 67.7-67.9) of elderly patients with good acute vision, there are areas that show reduced choroidial perfusion. In fact, the deposition of lipids in the Bruch's

Figure 67.7 Retinal fundus in an young (25 years of age) and healthy subject. In correspondence of the head of the optic nerve the ophthalmic artery is branched in four divisions for each quadrant of the retina. In this image the nasal superior and inferior branches are evident (field 40° corresponding to a magnification of about 5x).

Field Fundus Photos
Figure 67.8 Retinal fundus in an old (70 years of age) subject. The retinic vessels show a decreased calibre. We can see a distrophic zone in RPE (field 25° corresponding to a magnification of about 8x).

membrane leads to the degeneration of the elastic fibers and collagen, causing rigidity of these structures with consequent reduction of their compliance. These reductions in turn cause resistance of the choroidial vessels, edema, and reduction of blood flow. These events lead to a worsening of all the functions of the RPE, including the ability to transport the catabolites resulting from the phagocytosis of the photoreceptors.

Figure 67.9 Retinal fundus in a subject of 60 years affected by nonproliferating diabetic retinal pathology. The white spots are wax exudates, while the black ones are blood stains (field 40c corresponding to a magnification of about 5x).
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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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