Agerelated Changes Of The Foveal Cones

The cone density range between age 56 and 90 is quite limited (116,600 to 210,000 cones/mm2), with the oldest overlapping the lower limit of the younger donors. An area of 0.8 mm diameter centered on the fovea is the only part of the retina where there are more cones than rods. This region contains 31,200 cones/mm2 with a variability coefficient of only 12%, and the gradient of the linear regression with respect to age is not significantly different from zero. This data supplies evidence that the cone population in the central 2.8° remains stable during adult life; furthermore the topography of the cones does not show any relevant evidence, as already said, of age-related loss of cones in the central 28°. The extrafoveal cones are not more vulnerable to aging than foveal cones according to the hypothesis that the macular pigment, highly concentrated in the central 2°, is an antioxidant that improves the light-induced peroxidation of lipids, and also because a small quantity of this carotenoid is detectable outside the fovea. However, the overall stability of the total number of cones does not exclude the loss of a small number of these. As there is no evidence for a loss of cones of this magnitude, the increase in the distance between foveal cones does not significantly contribute to the age-related decline in visual resolution. The loss of acuity, therefore, may be explained by other changes in the visual system, including an age-related reduction of 25% in the number of ganglion cells that preside over the central 11° of the vision field. Also, recent evidence has shown that in the majority of cases, optical rather than retinal factors contribute to deficiencies in scotopic function, and therefore a reduction in sensitivity to spatial contrast at medium and high frequencies can be explained by a lower transfer modulation of the ocular medium in healthy elderly eyes. However, neuronal factors may play a role in other photoptic functions, such as the sensitivity to differences in luminosity (across the visual field) or spatial vision (for example, contrast sensitivity and visual acuity) considered at the mesopic or high scotopic level.

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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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