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Vascularity of mammalian retinae : a comparative anatomical study of mammals with and without intraretinal blood vessels

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posted on 2023-05-27, 08:30 authored by Buttery, Robert Gordon
The physical requirements necessary for the perception of light have produced peculiar adaptions to the way in which the eye is nourished. In many mammals there is a dual blood supply to the retina derived from both choroidal and intraretinal circulations. Interestingly, some species have only a choroidal blood supply. This study has addressed the coping strategies of those retinae which lack intraretinal blood vessels. Placental guinea pigs and diprotodont marsupial brushtail possums and sugar gliders, all of which lack retinal circulation (avascular retinae) have been compared with placental rats and polyprotodont marsupial quolls, Virginia opossums and Tasmanian devils, all of which possess intraretinal blood vessels (vascular retinae). Functional angiographic study has documented vascular patterns and demonstrated the close arteriovenous pairing within the polyprotodont marsupial retina. Avascular retinae are thinner than their vascular counterparts. The difference is not great (170Am versus 220gm): The limitation in thickness is borne by most retinal laminae but more so by those layers furthest from the choroidal supply. Morphological analysis suggests that spatial visual acuity is comparable in vascular and avascular species. Corrosion casting and microscopy of the ocular vasculature has shown that the choroid of the avascular species examined has no obvious morphological specialisations which might offset the lack of retinal vessels. However, the metabolic pathways within the inner layers of avascular retinae are markedly different, with limited oxidative metabolism as indicated by the activity of the mitochondrial enzyme, cytochrome oxidase. However, ATPase activity, as a measure of overall energy consumption, is known to be high within the inner layers of the avascular guinea pig retina (Ueno et al. 1981). This suggests that low cytochrome oxidase activity need not mean limited functional metabolic capacity. As a morphological accompaniment of oxidative activity, ultrastructural analysis would suggest that mitochondrial numbers may be reduced within the inner retinal layers of avascular retinae when compared with similar regions in vascular retinae. Central to these observations is the clinical question of whether the human retina can mimic the coping strategies of avascular retinae following pathological disruption of its intrinsic vasculature.

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Copyright 1990 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Library has additional copy on microfiche. Thesis (Ph.D.)--University of Tasmania, 1991. Includes bibliographical references (p. 271-308)

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