Uveoscleral outflow decreases with age in ocular normotensive humans

Purpose. Because the incidence of chronic open angle glaucoma and ocular hypertension increases with age, ocular normotensive volunteers were recruited to identify age-associated changes in aqueous humor dynamics. Methods. Normotensive subjects from two age groups were enrolled in the study: 1) those from 20 to 30 years of age (n=20) and 2) those 60 years of age and older (n=16). Aqueous flow and outflow facility were determined with fluorophotometry. Anterior chamber volume was determined with pachymetry. IOP was measured by pneumatonometry, tonographic outflow facility by pneumatonography and episcleral venous pressure by venomanometry. Uveoscleral outflow (Fu) was calculated mathematically. Results from the older age group were compared with those from the younger age group using unpaired, two-tailed, t-tests. Results. The older age group had a significantly (p<0.0001) smaller anterior chamber volume (175±11 versus 259±11 μl, respectively) and significantly (p<0.01) reduced Fu (0.09±0.19 versus 1.04±0.30 μl/min, respectively) compared to the younger age group. None of the other parameters were significantly different between the two age groups. Conclusions. There is a significant reduction in Fu in older, compared to younger subjects without elevated IOP. Since detectable in subjects even with normal IOP, reduced Fu may be responsible in part for the increased prevalence of ocular hypertension and chronic open angle glaucoma with increasing age.