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Stephen J. Cringle, Dao-Yi Yu, Valerie Alder, Er-Ning Su; Light and Choroidal Po2 Modulation of Intraretinal Oxygen Levels in an Avascular Retina. Invest. Ophthalmol. Vis. Sci. 1999;40(10):2307-2313.
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purpose. To determine the influence that choroidal oxygen level and outer
retinal oxygen demand have on oxygen availability to the inner retina
when the choroid is the only source of retinal oxygenation. This
condition prevails in avascular retinas and in vascularized retinas
suffering vascular occlusion.
methods. Oxygen-sensitive microelectrodes were used to measure the oxygen
tension as a function of depth in the naturally avascular retina of
anesthetized and mechanically ventilated guinea pigs
(n = 6). Choroidal Po 2 was
manipulated by varying the ventilation gas mixture, and outer retinal
oxygen consumption was modulated by light-dark adaptation. Individual
Po 2 profiles were fitted to a multilayer
mathematical model of Po 2 distribution, and
pairs of profiles at different choroidal Po 2 levels, or under light and dark conditions, were fitted to an
intraretinal Po 2 difference model. Both models
reflect the purely choroidal supply of retinal oxygenation.
results. An increase in choroidal Po 2 produced an
equivalent increase in all retinal layers. Light induced a decreased
oxygen consumption in the region of the inner segments of the
photoreceptors, which resulted in a significant increase in
Po 2 in this layer, flowing on unattenuated to
all inner retinal layers. The intraretinal Po 2 distribution and the light- and ventilatory-induced changes in
Po 2 were consistent with theoretical
predictions of the mathematical models.
conclusions. The present experimental studies confirm that when the choroid is the
only source of retinal oxygenation, the full effect of increased
choroidal oxygen level or reduced uptake in the outer retina passes
through to the inner retinal layers if the oxygen utilization by the
inner retina remains constant.
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