Abstract
Purpose: :
The main objective of this study was to evaluate the oxygene regulation in retinal blood vessels and optic nerve capillaries, as the oxygen consumption by the retina, in a stress situation, engendered by an hypoxic systemic condition.
Methods: :
Ten young healthy non-smokers subjects participated in the study. Using a continuous and real time spectro-reflectometry technique (Diaconu 2009), we recorded the blood oxygenation changes in the retinal arteries and veins, as in optic nerve micro-capillaries structures, during conditions of hypo-oxygenation, created with a Medisoft ventilation system. An experimental session consisted of breathing 21% oxygen for one minute, 15% oxygen hypoxic breathing condition for five minutes, then 21% oxygen for one minute. The heart rate and the systemic blood oxygenation changes were monitored with a pulse oxy-meter on the finger. Retinal oxygen consumption was estimated from the difference in blood oxygenation between the main temporal inferior artery and its corresponding vein. The main interest of the study was to compare ocular and systemic oxygenation, and oxygen consumption in the retina, in order to understand ocular vascular regulation.
Results: :
The results show that the blood oxygenation in the eye vessels decreases 30 seconds after the 15 % O2 ventilation condition is established. A fall of 6% in systemic arterial blood oxygenation induces an increase of 10% of heart rate and a simultaneous reduction of 5 % in blood oxygenation in the optic nerve head, and the retinal main arteries and veins.
Conclusions: :
In intense systemic hypoxia condition, this data does not show any blood oxygenation regulation mechanism in the optic nerve head micro-capillaries nor in the retinal arteries and veins. Hypoxia leads indeed to oxygenation decrease even in the optic nerve which is known to be very sensible to oxygenation privation. However, oxygen consumption in the retina remains stable despite lack of arterial blood oxygen. This could lead to the hypothesis that, even if regulation mecanisms are absent or overwhelmed in an acute condition, the retina can continue to assure its fonction adequately, at least for a short period of time. To know if regulation mecanisms could occur with less intense systemic oxygenation drop remains to be elucidated. This technique could be used further to investigate modifications of oxygenation metabolism in retinal or optic nerve diseases, for instance in glaucomatous patients.
Keywords: blood supply • hypoxia • optic nerve