Le vieillissement de l’oeil chez l’animal

Abstract

Ageing is the effect of time that predisposes beings to death. The study of the biology of ageing shows that certain molecular phenomenons are responsible for cellular and tissue modifications, including an increase in collagen rigidity, namely at the blood vessel level, in addition to an accumulation of “old” un-degraded molecules. In addition, oxygen, which is essential for life, gives rise to free radicals which attack different cellular molecules, DNA, lipids and proteins once it is metabolized. The brain is particularly susceptible to the mechanisms, given that it is a tissue that consumes high quantities of oxygen in order to carry out neuronal activity. Furthermore, the lack of neuronal renewal makes this tissue vulnerable to such injury. The eye is an example of such a vulnerable area, since retinal tissue is the highest consumer of oxygen and glucose. The choroid is responsible for supplying the retina with oxygen and glucose through numerous fenestrated blood vessels that allow photoreceptor oxygen concentrations to reach levels close to that found in the blood. The accumulation of glycation products in the lens and the irido-corneal angle favors the development of cataracts and a «thickening» of the trabeculum which results in a reduction of aqueous humor leakage that leads to an increase in intra-ocular pressure, and finally glaucoma. At the ocular surface, ageing of the extracellular stromal matrix is characterized by the increase in interfibrillary and intramolecular spacing of collagen which leaves room for the accumulation of glycation products. The eye is an organ which is particularly sensitive to the effects of ageing. An ophthalmic exam allows for the detection of various markers of ageing at the ocular surface, the irido-corneal angle, the lens and the fundus. These exams give information on the physiologic state of the ageing animal. Finally, it is interesting to note that, similar to man, the life expectancy of pets is increasing, thus revealing the same type of pathologies related to ageing. The eye is an «observation window» which is easily accesible in terms of not only the microcirculation, but also of the cerebral neurological state.