Pathophysiology of the blood-retinal barrier in experimental diabetes. Vitreous fluorophotometry using carboxyfluorescein and fluorescein.

Carboxyfluorescein resembles fluorescein in size and spectral characteristics but is much less lipid soluble. Both dyes were used to differentiate between two groups of factors that influence penetration across the blood-retinal barrier: (1) factors that depend on lipid solubility, such as the area of the barrier, and (2) factors independent of lipid solubility, such as opened intercellular junctions or necrotic cells. Vitreous fluorophotometry was performed on normal and diabetic rats after injection of either dye. After the results were adjusted for sources of error, midvitreous-plasma dye ratios for carboxyfluorescein and fluorescein were of the same order of magnitude in normal rats. Ratios for both dyes increased in diabetic rats, and the increases were similar in magnitude. Our results suggest that lipid solubility contributes little to inward transport of these dyes in both the normal and diabetic states.