QUANTITATIVE VITREOUS FLUOROPHOTOMETRY APPLYING A MATHEMATICAL-MODEL OF THE EYE

  • 1 January 1985
    • journal article
    • research article
    • Vol. 26  (5) , 698-710
Abstract
A slit-lamp fluorophotometric method is presented that permits calculation of a blood-retinal barrier permeability to fluorescein (P) and a diffusion coefficient for fluorescein in the vitreous body (D). Calculations are performed by relating the time course of the free.sbd.not protein bound.sbd.fluorescein concentration in the bloodstream with the fluorescein concentration profile in the vitreous body. The combination is performed automatically on a computer by applying a simplified mathematical model of the eye. P refers to the area of the barrier of the model eye. In a group of 6 normal persons, the mean P was (1.1 .+-. 0.4) .times. 10-7 cm/s, while in 6 diabetic patients with background retinopathy and macular edema the mean P was (7.1 .+-. 3.8) .times. 10-7 cm/s. The mean D was (7.4 .+-. 3.4) .times. 10-6 cm2/s in the normal group and (9.6 .+-. 2.0) .times. 10-6 cm2/s in diabetic patients, corresponding as a 1st approximation to free diffusion in H2O. Model calculations show that knowing the fluorescein concentration in the bloodstream is considerably significant for the calculation of the permeability, contributing factors up to 50%. For the low-permeation situation, subtraction of the preinjection scan contributes a factor of 50% for permeability and diffusion coefficient. The exact placement in the vitreous body of the concentration profile, by applying a formalism that transforms slit-lamp movement to intraocular distance, contributes a factor of 20% on the diffusion coefficient. The permeability obtained with the model can be calculated as the ratio between area of vitreous and plasma fluorescein concentration curves within 20%. Active transport of fluorescein across the blood-retinal barrier in the direction of vitreous to blood does not seem to be significant within the first 2 h after fluorescein injection.

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