No abstract

The present study indicates that lower choroidal perfusion is a risk factor for the development of CNV in the fellow eye of patients with unilateral CNV.

Aim: To determine the effects of various mixtures of O 2 and CO 2 on retinal blood flow in healthy subjects. Methods: A randomised, double masked, four way crossover trial was carried out in 12 healthy male non-smoking subjects. Gas mixtures (100% O 2 , 97.5% O 2 + 2.5% CO 2 , 95% O 2 + 5% CO 2 , and 92% O 2 + 8% CO 2 ) were administered for 10 minutes each. Two non-invasive methods were used: laser Doppler velocimetry (LDV) for measurement of retinal blood velocity and fundus imaging with the Zeiss retinal vessel analyser (RVA) for the assessment of retinal vessel diameters. Arterial pH, pCO 2 , and pO 2 were determined with an automatic blood gas analysis system. Retinal blood flow through a major temporal vein was calculated. Results: Retinal blood velocity, retinal vessel diameter, and retinal blood flow decreased during all breathing periods (p <0.001 each). Administration of 92% O 2 + 8% CO 2 significantly increased SBP, MAP, and PR (p <0.001 each, versus baseline), whereas the other gas mixtures had little effect on systemic haemodynamics. Addition of 2.5%, 5%, and 8% CO 2 to oxygen caused a marked decrease in pH and an increase in pCO 2 (p <0.001 versus pure oxygen). Conclusions: Breathing of pure oxygen and oxygen in combination with carbon dioxide significantly decreases retinal blood flow. Based on these data the authors speculate that hyperoxia induced vasoconstriction is not due to changes in intravascular pH and cannot be counteracted by an intravascular increase in pCO 2 . E levated arterial blood oxygen tension (pO 2 ) results in vasoconstriction and a pronounced decrease in retinal blood flow.1-3 The mechanisms underlying O 2 induced vasoconstriction are not completely clear. We have previously shown that endothelin receptor mediated vasoconstriction plays a part in hyperoxia induced vasoconstriction in healthy subjects. 4 This is in keeping with several animal experiments, 5 6 in which thromboxane A 2 , 20-HETE, and cytochrome P-450 were identified as other mediators of hyperoxia induced vasoconstriction. Another factor which may contribute to the reduction in retinal blood flow during hyperoxia is intracellular and extracellular alkalosis. In vitro experiments indicate that the contractile tone of pericytes strongly depends on the pH. 7-9 Pericytes are, however, assumed to play a part in the regulation of vascular resistance in the retina. Hence, one may speculate that pericytes participate in the regulation of retinal capillary blood flow in response to changes in the pH.In the present study we examined the effects of various mixtures of O 2 and CO 2 (hyperoxia-hypercapnia) on retinal blood flow in healthy subjects. Previous studies investigating this topic were contradictory. [10][11][12][13][14] This may be related to the fact that none of these trials was masked or randomised. Moreover, in none of these clinical studies in healthy subjects was retinal perfusion assessed continuously during the inhalation periods and time dependent effects may therefore have been missed. METHODS SubjectsThe...

These data indicate that NO plays an important role in the regulation of choroidal blood flow during isometric exercise.