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Robert A. Linsenmeier, Lissa Padnick–Silver; Metabolic Dependence of Photoreceptors on the Choroid in the Normal and Detached Retina. Invest. Ophthalmol. Vis. Sci. 2000;41(10):3117-3123.
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purpose. This article assesses the hypothesis that the high blood flow rate and
low O2 extraction associated with the choroidal circulation
are metabolically necessary and explores the implications of the
spatial relationship between the choroid and the photoreceptors for
metabolism in the normal and detached retina.
methods. The O2 distribution across the retinal layers was
previously measured with O2-sensitive microelectrodes in
cat. Profiles were fitted to a diffusion model to obtain parameters
characterizing photoreceptor O2 demand. This was a study of
simulations based on those parameters.
results. Photoreceptor inner segments have a high O2 demand
(QO2), and they are far (20 to 30 μm) from the
choroid. These unusual conditions require a large O2 flux
to the inner segments, which in turn requires high choroidal oxygen
tension (PO2), high choroidal venous saturation
(ScvO2), low choroidal O2 oxygen extraction per
unit volume of blood, and a choroidal blood flow (ChBF) of
at least 500 ml/100 g-min. Movement of the inner segments further from
the choroid, which occurs in a retinal detachment, severely reduces the
ability of the inner segments to obtain O2, even for
detachment heights as small as 100 μm. Depending on detachment height
and assumptions about choroidal and inner retinal PO2 during elevation of inspired O2 (hyperoxia), hyperoxia is
predicted to partially or fully restore photoreceptor QO2 during a detachment. conclusions. The choroid is not overperfused, but requires a high flow rate to
satisfy the normal metabolic demand of the retina. Because the
oxygenation of the photoreceptors is barely adequate under normal
conditions, detachment has serious metabolic consequences. Hyperoxia is
predicted to have clinical benefit during detachment.
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