Measurement of Aqueous Dynamics in Low Tension Glaucoma

Glaucoma is usually associated with elevated intraocular pressure, but some patients seem to lose vision from glaucoma despite normal pressures. We hypothesize that some of these people (who have “low-tension glaucoma”) have intermittent elevation of pressure because of poor outflow of aqueous humor coupled with an instability of their aqueous production. During periods of low production, their intraocular pressures may be normal, despite the poor outflow. This is most likely their normal state. During periods of normal production, their intraocular pressures would most likely be high, high enough to be damaging to the optic nerve. We wonder if the low production could be due to lack of blood flow to the eye, for if this were the case, it could explain an instability of pressure and an increased susceptibility of the optic nerve to pressure. In this grant application, we propose to study a group of subjects with low- tension glaucoma, a group with open angle glaucoma (“high tension glaucoma”) and a group of normal subjects. The aqueous humor production will be measured during both day and night, and the intraocular pressure and the resistance to outflow of aqueous humor will be measured. We will compare the findings between the above mentioned groups to see whether low-tension glaucoma is associated with abnormally low aqueous humor production or not, and if the resistance to outflow is higher or not. We also will be able to see if the normal diurnal fluctuation in aqueous humor production exists in patients with low-tension glaucoma and high-tension glaucoma, or if there is a different aqueous flow pattern in these diseases.