Abstract
Purpose: :
This study evaluates the effects of brimonidine on daytime and nighttime aqueous humor dynamics in patients with ocular hypertension (OHT).
Methods: :
Thirty patients with OHT (58.6±9.2 years of age) were enrolled in this randomized, double-masked, crossover study. Participants self-administered 0.2% brimonidine or placebo three times a day for 6 weeks. At the end of each 6 week period, aqueous humor dynamics were studied at one daytime and one nighttime visit. Measurements included aqueous flow by fluorophotometry, outflow facility by tonography, episcleral venous pressure (Pev) by venomanometry and seated and supine intraocular pressure (IOP) by pneumatonometry. Measurements of IOP were made at 9 AM, 11 AM, 1 PM, 3 PM, 9 PM, 11 PM, 1 AM, and 3 AM. Uveoscleral outflow (Fu) was calculated mathematically using the modified Goldmann equation. The results were compared by two-tailed paired t-tests. P values< 0.05 were considered statistically significant.
Results: :
When treated with vehicle, nighttime supine Pev (11.2±1.6 mmHg) was significantly higher than daytime seated Pev (10.2±1.5, p=0.002), and aqueous flow and uveoscleral outflow were lower (by 0.79 µl/min, p<0.01 and 1.06 µl/min, p=0.01, respectively) at night than during the day. Compared with vehicle treatment, brimonidine significantly lowered seated IOP at 9 AM, 11 AM, 9 PM and11 PM and supine IOP at 9 AM, 11 AM (by 1.5 to 2.2 mmHg, p<0.01) but had no effect on IOP at 1 AM and 3 AM. Brimonidine significantly increased uveoscleral outflow during the daytime (by 0.84 µl/min, p<0.01) only and had no effect on daytime and nighttime aqueous flow, outflow facility or Pev.
Conclusions: :
Brimonidine treatment for 6 weeks reduced habitual IOP during the day but not at night. The daytime IOP reduction is associated with an increase in daytime uveoscleral outflow. The lack of IOP effect at night can be explained by failure to increase uveoscleral outflow, nighttime physiological changes in aqueous humor dynamics in patients with OHT may diminish the pharmacological effect of brimonidine making this drug ineffective at night.
Clinical Trial: :
University of Nebraska, NCT01144494
Keywords: aqueous • intraocular pressure