Fluorescein and fluorescein glucuronide in the vitreous body of diabetic patients

Fluorescein (F) and fluorescein glucuronide (FG) were determined in the vitreous of four diabetic patients by a double-filter slit-lamp fluorophotometric technique. Determinations were performed 60-80 min after i.v. injection of fluorescein. F and FG were also determined in plasma ultrafiltrate 5, 15, 30, 60 and 120 min after injection by high-pressure liquid chromatography. The concentration of FG in the vitreous was 3 times that of F. After correction for plasma concentrations of FG higher than those of F, the penetration index of FG through the blood-retinal barrier was found to be twice the penetration index of F. This is not what would be expected if passive transport alone were involved. Accordingly, it is suggested that active transport mechanisms contribute to the movement of F and FG across the blood-retinal barrier.