Vasoconstrictive effects of sodium fluorescein on retinal vessels is increased by light exposure

Purpose: To determine whether clinically relevant doses of sodium fluorescein produce changes in vascular tone in retinal arterioles and veins and whether any such effects were light dependent. Methods: Segments of porcine retinal arterioles and veins were dissected, cannulated, and perfused and their outer diameter monitored during intraluminal application of increasing doses (10(-10) to 10(-3) g/ml) of sodium fluorescein under either brightly lit (350 lux) or dimly lit (4 lux) conditions. The significance of any induced change in vessel diameter was assessed in relation to the initial vessel diameter. Results: At the higher light level, sodium fluorescein produced a significant dose-dependent contraction in porcine retinal arterioles and veins with a threshold of 10(-5) g/ml and 10(-9) g/ml sodium fluorescein, respectively. At the maximal dose tested (10(-3) g/ml), vessel diameter was reduced to similar to 85% of the initial vessel diameter in retinal arterioles and veins. Under dimly lit conditions, the vasoconstrictive effect of sodium fluorescein was still evident but the constriction was significantly smaller (p < 0.05) in both arteries and veins, reaching similar to 91% and 93%, respectively. Conclusions: Sodium fluorescein induced light-dependent vasoconstrictive effects on the retinal vasculature of the pig. Should a similar effect be present in human retinal vessels, then reduced illumination level may limit the vasoconstrictive effects of sodium fluorescein when used in routine ophthalmic examinations.