Intraretinal oxygen distribution and choroidal regulation in the avascular retina of the guinea pig. Yu, Dao-Yi, Stephen J Cringle, Valerie A Alder, Er-Ning Su, and Paula K Yu. Lions Eye Institute, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia 6009
APStracts 2:0409H, 1995.
Oxygen sensitive microelectrodes were used to measure oxygen tension as a function of depth through the retina and choroid of anaesthetised and artificially ventilated guinea pigs. The guinea pig retina is of particular interest because it has a typically mammalian structure but no retinal circulation, relying totally on choroidal delivery of oxygen and other nutrients. Measurements of intraretinal oxygen distribution in an avascular mammalian retina have not previously been reported. Under normal ventilation conditions oxygen tension decreased monotonically from the choroid (33.6 + 2.9 mmHg, n=11) to near zero levels (0.4 + 0.1 mmHg) at the retina/vitreous boundary. The inner half of the retina had an average oxygen tension of only 0.6 + 0.1 mmHg. Stepwise increases in inspired oxygen (20-40 -60-80-100%) had surprisingly little effect on choroidal oxygen tension. Rapid changes (20-100%) produced overshoot type responses in the choroid before recovering to levels only slightly above those found in normoxia. This indicates the presence of an active oxygen regulatory mechanism in the guinea pig choroid. Addition of carbon dioxide (5%) to oxygen ventilation appeared to break down this control mechanism and led to dramatic and sustained increases in oxygen tension throughout the retina and choroid. The demonstration of an oxygen regulating mechanism in the guinea pig choroid that maintains choroidal oxygen tension well below that in the systemic arterial blood, coupled with the observation of very low oxygen levels throughout the inner retina, suggests that the oxygen requirement of the inner retina in the guinea pig is small and that oxygen levels in the choroid are deliberately constrained. 

Received 29 March 1995; accepted in final form 6 September 1995.
APS Manuscript Number H293-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.