Regulation of Episcleral Venous Pressure

Progress Updates

This project focused on the way the intraocular pressure, or "IOP" reacts to changes in posture. When humans lay down, the IOP rises, but much less than it should. Dr. Kiel’s team suspected this is because the pressure in the veins just outside the eye is tightly regulated. This episcleral venous pressure, or "EVP," is difficult to measure in humans, and so they studied it in an animal model. In the past two years, the team has confirmed that the IOP is protected in their animals as it is in humans when they lay down, and that this is not due to decreased aqueous production. Instead, the team found that when they simulate lying down in their animals, the venous pressure and the IOP increase by a similar, small amount that is significantly less than expected. They suspect the EVP is controlled by a neural reflex, but their tests so far indicate that the sympathetic and parasympathetic nerves (components of the autonomic nervous system) are not involved. They have also tested other possible nerves and local mechanisms that might be responsible, and have found that some of them may be responsible. What makes this work potentially important is that humans spend roughly a third of their lives lying down. If there is a neural reflex that controls EVP and so protects IOP, what if it fails? Does this cause the IOP to go up too high when someone lays down and so contribute to glaucoma? Or can drugs mimic the reflex to decrease EVP and provide a new way to lower IOP and treat glaucoma? Dr. Kiel’s team will continue studying EVP with NIH support in order to find out.