Routes of clearance of radioactive water from the rabbit vitreous.

Abstract

SUMMARY The movement of water to and from the vitreous across the retina and pigment epithelium is important in relation to an understanding of such conditions as retinal detachment and its surgical cure, central serous retinopathy, and retinal oedema. Experiments were carried out to determine the main routes for removal of water injected into the vitreous and to see if the removal could be explained on the basis of diffusion or whether bulk flow was also implicated. 25 ,uCi of 3H20 in 25 IlI were injected into a central position in the vitreous humour of living rabbits under general anaesthesia. For 9 animals blood was collected from one of the 4 vortex veins draining the choroid and the radioactivity in the samples measured. For another 6 rabbits similarly injected the radioactivity in samples of aqueous humour was determined. The percentage of injectate recovered from the vortex vein blood ranged between 13% and 38%, mean 25+±3%. The percentage of injectate recovered from the aqueous humour ranged between 1 2% and 5 2%, mean 2-8±0-6%. Analysis of the time course of isotope activity in the samples revealed a mean transit time from the mid vitreous to the choroid of 32+2 minutes, and from the mid vitreous to the anterior chamber of 84±3 minutes. By means of a computer model it was calculated that diffusion alone could effect this transfer; if active transport were involved in the transport of 3H20 to the choroid, this was not a limiting factor under the conditions of the experiment. reported work on molecular movement from the vitreous has used a variety of tracers, some of which might have been subject to the processes of active transport, or differed from water in intermolecular interactions or in molecular size.Diffusional exchange with the water in the anterior chamber, which is largely cleared by bulk flow through the outflow apparatus, is another factor which might influence the clearance of water from the vitreous.As part of a study of water movement in the eye, experiments were carried out to: (1) determine the main routes of clearance of 3H20 injected into the midvitreous of living rabbit eyes and to quantify the movement via each of these routes; (2) determine by comparison with a mathematical model whether any detected movements of water could be explained entirely by diffusion or whether active transport or bulk flow were involved. The results of these studies are presented in this paper. 145

The Retinal Pigment Epithelium in Visual Function

“…This establishes the need for constant removal of water from the retina. Water in the inner retina is transported by Mü ller cells (411,418), and water in the subretinal space is eliminated by the RPE. Furthermore, the water transport is required for close structural interaction of the retina with its supportive tissues in establishment of an adhesive force between RPE and the retina (308,366,370).…”

Noninvasive Detection of Ganciclovir in Ocular Tissue by Raman Spectroscopy: Implication for Monitoring of Drug Release

“…Various studies have shown that when substances are administered as intravitreal injections in the eye, some of the substance appears in the anterior chamber (10,11). The present study was designed to determine if confocal Raman (Conforam) spectroscopy could be used to assess the concentration of ganciclovir in the anterior chamber in a noninvasive manner.…”

Intravitreal controlled release of dexamethasone from engineered microparticles of porous silicon dioxide

“…The cov-OPS:DEX particles used in this study can easily pass through a 27-gauge needle, and can place the drug loaded particles into vitreous at the posterior. Due to the fact that vitreous water exits mainly through the retina into the choroid (over 80%), (Moseley et al, 1984) the drug placed in the posterior vitreous would be the most effective for macular diseases and would bring the least complications, such as high IOP and cataract. From the current in vitro drug release, the covalent conjugation of Dex to pSiO 2 led to a sustained Dex release for at least 90 days, with a mean concentration of 2480±2549 ng/mL during first 9 days, 224±141 ng/mL from day 14 to day 40, and 24±15 ng/mL during the last segment of 45 days (from day 45 to day 90).…”