Outflow facilities through Descemet's membrane in rabbits

Abstract.

Background: The outflow pathway in viscocanalostomy, a new procedure in glaucoma surgery, is unclear; however, outflow through Descemet's membrane has been postulated. This study evaluates outflow rates through Descemet's membrane at different IOP levels in rabbits. Methods: 51 Descemet's membranes without endothelium from enucleated rabbit eyes were installed in a double-ring system, the Minuth sheet. Different intraocular pressure levels (20, 25, 30, 40, 50 mmHg) were applied to one side of the system. The system was filled with balanced salt solution. The total amount of fluid percolating through Descemet's membrane was measured after 12 h. Based on this, flow rates were calculated. The area of Descemet's membrane was 6.9 mm². Results: At the pressure of 20 mmHg the flow rate was less than 0.003 µl/min. At pressures above 30 mmHg flow rates ranged from 0.04 µl/min to 0.15 µl/min with a mean of 0.09 µl/min. To achieve pressure control at high pressures, an area of at least 150 mm² of Descemet's membrane would be needed. Conclusion: Descemet's membrane provides good outflow resistance in rabbit eyes. Based on our results for pressure control by outflow through Descemet's membrane only, at least the whole corneal area is needed. If the same is true in humans, additional outflow sources are necessary in cases of viscocanalostomy.