Study of Choroidal Blood Flow by Comparison of SLO Fluorescein Angiography and Microspheres

Abstract

Choroidal hemodynamics estimated with parameters describing the dye build-up curves obtained with video fluorescein angiography, were compared with a classical regional blood flow measurement: radioactively labelled microspheres. Video fluorescein angiograms (Rodenstock's SLO 101) and microspheres blood flow measurements were made in 13 anaesthetized pigmented rabbits. Ocular perfusion pressures were varied from 60 to 15 mmHg by changing the intraocular pressure. The angiographically derived dye build-up curves were described by means of an exponential model. One of the model parameters is the time constant τ theoretically reflecting local blood refreshment time. Labelled microspheres act as a non-recirculating blood flow indicator, enabling the estimation of regional blood flows. The relation between choroidal blood flow and perfusion pressure is nearly linear, suggesting the passive nature of choroidal vasculature. There is a significant correlation between τand microspheres flow ( R=0.67, P<0.01). According to the rheological model the product of blood flow and τcorresponds to the relevant blood volume. Hence, a function for the volume of the choriocapillaris as a function of perfusion pressure was established. The model parameter τcan be interpreted as the local blood refreshment time. Since the parameter τ, unlike microspheres, can be used clinically, τmay be used to retrieve information on choroidal hemodynamics in clinical practice. Information on the spatial distribution of choroidal hemodynamics is also obtained.