Posterior vitreous fluorophotometry. I. Description of a new analysis procedure and results in normal subjects

P. M. Bungay, M. S. Roy and R. F. Bonner
Division of Research Services, National Eye Institute, Bethesda, MD 20892.

A new automated analysis procedure was used to evaluate the apparent blood-retinal barrier permeability (mean +/- SD = 1.31 = 0.31 X 10(-7) cm/s at 60 minutes after intravenous dye administration) and the effective diffusivity (mean +/- SD = 0.88 +/- 0.40 X 10(-5) cm2/s) for fluorescein in the vitreous of 21 normal subjects. The analysis improvements include (1) use of an individualized convolution (spread) function for each eye in comparing simulated and experimental scans, (2) separation of vitreous and chorioretinal fluorescence, and (3) precise determination of vitreous position relative to the retina. The average reproducibility in six subjects was 23% for permeability and 22% for diffusivity based on repeated determinations separated in time by at least a week. Diffusivity values, but not permeability values, significantly associated in comparisons of first and second determinations, suggesting permeability may fluctuate in time while diffusivity remains relatively constant. The fluorescence at 3 mm anterior to the retina (commonly employed as a measure of blood-retinal barrier leakiness) was strongly associated with diffusivity. In contrast, the anticipated association between permeability and 3-mm fluorescence was weak or absent.