The effects of brimonidine on daytime and nighttime intraocular pressure (IOP) and aqueous humor dynamics were evaluated in volunteers with ocular hypertension (OHT).
Thirty participants with OHT (58.6±1.7 years old, mean±SEM) were enrolled into this randomized, double-masked, cross-over study. For 6 weeks, participants self-administered 0.2% brimonidine or placebo 3 times daily. During daytime and nighttime visits, measurements included aqueous flow (F a) by fluorophotometry, outflow facility (C) by tonography, episcleral venous pressure (P ev) by venomanometry, and seated and supine IOP by pneumatonometry. Uveoscleral outflow (U) was calculated mathematically.
When treated with placebo, nighttime supine P ev (11.2±0.25 mm Hg) was higher (P<0.05) compared with daytime seated P ev (10.2±0.25 mm Hg), and F a and U were significantly reduced at night. Brimonidine significantly lowered seated IOP at 9:00 AM and 11:00 AM, 9:00 PM and 11:00 PM and supine IOP at 9:00 AM and 11:00 AM. Brimonidine increased U at 9 AM and 11 AM (P<0.01) and had no effect on daytime and nighttime F a, C, or P ev.
In subjects with OHT, brimonidine treatment for 6 weeks significantly reduces seated IOP during the day by increasing uveoscleral outflow. The lack of IOP effect at night can be explained by failure to overcome a normal nighttime reduction of uveoscleral outflow.
Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, NE
Supported by the American Glaucoma Society MAPS grant (Research to Prevent Blindness).
Disclosure: The authors declare no conflict of interest.
Reprints: Carol B. Toris, PhD, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, NE 68198-5840 (e-mail: firstname.lastname@example.org).
Received May 2, 2013
Accepted March 4, 2014