Long-term kinetic vitreous fluorophotometry.

Fluorophotometric measurements of vitreous and plasma fluorescence were performed in 14 normal subjects up to 24 h after injection of a single intravenous dose of sodium fluorescein. The data were subjected to a kinetic two-compartmental analysis, including the determination of the transfer rate constants between the central and the peripheral compartment (K12 and K21) as well as between the central and vitreous compartment (K(in) and K(out)). In the central compartment (plasma) a mean terminal disposition rate constant (beta) of free fluorescein of 0.23 h-1 was found, corresponding to a half-life of 3.01 h. The vitreous fluorescence reached a maximum 2-5 h after the injection and then declined monoexponentially and very slowly (t1/2 = 9.6 h). The rate constant of permeation into the eye (K(in)) was found to be 0.66 h-1, while the rate constant of elimination of fluorescein from the vitreous was 0.072 h-1 (K(out)). Kin was found to be significantly higher than K12, presumably indicating an active transport mechanism for fluorescein located at the blood-ocular barrier. K(out) was significantly lower than K21, reflecting a slow vitreous elimination of fluorescein. A permeability index defined as the percentage ratio between the areas under the vitreous and the plasma concentration curves was found to be 3.5%, illustrating the poor penetration of fluorescein into the vitreous. Kinetic long-term fluorophotometry appears to be a promising new tool in the study of the blood-ocular barrier.