Introduction

The majority of elderly people suffer from deficiencies in both photopic (Owsley and Burton, l99l) and scotopic (Sturr and Hannon, l99l) vision, not related to any organic pathology, but rather as part of the general decline in all the functions of the body. Based on the theory of physical deterioration, it is believed that the body is placed under stress and injury, both extrinsic (dependent on the environment) and intrinsic (dependent on biological processes). This damage derives from small, highly reactive molecules known as free radicals (Armstrong, l984), which are produced during normal metabolic processes and are associated with important cellular functions (Brizee andOrdy, l98l). Of these damaging agents, we shall consider reactive oxygen intermediates, capable of inducing oxidative stress. In addition, peroxy-nitrites, endogenic alkylating agents, and aldehyde products, resulting from the oxidation of lipids, also have the capacity to damage macromolecules (protein and lipid complexes, DNA, etc.) (Dykens, l999). Macromo-lecular damage results in cellular dysfunction manifested by nuclear instability, inappropriate cell differentiation, and consequent cell death (necrosis or apoptosis) (Handelman and Dratz, l986). These age-related changes of the retina primarily cause a loss of visual acuity and impairment of color discrimination as well as reduction of the visual field. Impairment of visual functions in aged subjects has long been considered the consequence of opacity of the dioptric media, whereas little attention has been paid to the retinal age-related changes. In light of our present findings, we can hypothesize that the fall in visual acuity occurring in old age is influenced, at least in part, by the age-related changes observed in human retinal tissues (Cavallotti et al., 2004). In fact, our group studied the Scanning Electron Microscopic (SEM) features of the human retina. For a detailed evaluation of the effects of aging on retinal morphology, a quantitative analysis of images was performed for obtaining morphometrical data. Our findings underlined that the human retina can be considered an optimal model for studies on neuronal maturation and/or neuronal aging, being particularly sensitive to age-related changes and to senile decay.

This chapter discusses the following:

• Morphological and functional organization of the human retina

• Choroid-retinal complex (choroid, Bruch's membrane, basal membrane, retinal pigmented epithelium)

• Neuronal cells of the retina

• Glial cells of the retina

• Retinal vessels

Handbook of Models for Human Aging

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• Aging of the whole retina (experimental results)

• Aging of the choroid-retinal complex

• Aging of neuronal cells of the retina

• Aging of glial cells of the retina

• Aging of retinal vessels

• Age-related diseases of the human retina

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