ABSTRACT
The morphological changes that accompany degenerative processes in the neural retina tend ultimately to assume a common pattern irrespective of their cause. Loss of neurons is followed by a net loss of tissue volume with replacement by a minor reactive proliferation of astrocytes or by cystoid changes within a network formed by the supporting Mu¨ller cells. With age there is a gradual nonpathological dropout of retinal ganglion cells at an approximate rate of 5000 per year resulting in a decrease in the fovea of about 16% from the second to the sixth decade (10). Photoreceptors, particularly the rods, are also vulnerable to loss during aging, but the ratio of photoreceptors to retinal pigment epithelium (RPE) cells remains the same, suggesting parallel loss of these closely apposed cells (10). The human macula comprises a cone-dense fovea encircled by a roddense parafovea. Throughout adult life, the cone density is maintained in the fovea however in the same time period the rod parafoveal density reduces by 30% (5). Loss of neurons in this way is accompanied by loss of the foveal reflex, due to shallowing of the foveal depression and enlargement of the capillary-free zone at the fovea.
