LOCAL PRESSURE EFFECTS ON VITREOUS KINETICS

Fluorescein (F) or carboxyfluorescein (CF) was injected subconjunctiva lly in rabbits and its penetration into and subsequent loss from the v itreous body and anterior segment was measured. Pressure was applied o ver the site of the injected dye, sufficient to close down the local c horoidal circulation. This raised the penetration of F about 30 times and delayed its loss, and raised the penetration of CF about seven tim es without affecting its loss rate, Cooling the tissue, in addition to local pressure, had little additional effect on the penetration. When F was made to penetrate by transcleral iontophoresis, pressure over t he site had no effect on its kinetics. This behavior was compared with the predictions by a mathematical model in which the dye was released as a pulse at the inside of the retina and then diffused freely in th e vitreous, loss occurring at the retinal surface by an outward transp ort process. Two experimental observations, the time at which the fluo rescence behind the lens reached its peak and its subsequent loss rate , were related in a graphical representation to two physiological para meters, the rate of diffusion of the dye in the vitreous body and the outward permeability of the retinal layer. In some sets of experiments , particularly those in which iontophoresis was used, the kinetics con formed well to the predictions of this model. In other cases, the agre ement was poor, and mechanisms such as storage of dye in the retina an d its penetration into the vitreous by an anterior pathway appear to p lay a role.