Currently, the only effective treatment to prevent disease progression is lowering of the intraocular pressure (IOP).2 Usually, clinical IOP measurements are performed during the day with little information collected on nocturnal IOP. A recent surge of interest in nocturnal IOPs stems from the hypothesis that significant glaucomatous damage may occur at night.4,5 In response, some investigators have advocated particular classes of glaucoma medications based on their nocturnal IOP effects.6-8 The most efficacious drug on the market may not be the preferred treatment if it is ineffective at night. Therefore, the understanding of nighttime IOP and the aqueous humor dynamics that control it has important scientific, clinical, and commercial implications.
Previous research on glaucoma medications has been limited to the effects of ocular hypotensive drugs on 24-hour IOP or daytime aqueous humor dynamics. Few studies have evaluated nocturnal aqueous humor dynamics. The investigators recently completed studies of day and night differences in aqueous humor dynamics in patients treated with drugs from three different classes that include a prostaglandin analog, a beta blocker and a carbonic anhydrase inhibitor. The current study is designed to elucidate the physiological mechanisms driving the efficacy of brimonidine, an alpha 2 adrenergic agonist, throughout the 24-hour period, i.e. circadian rhythms in aqueous humor dynamics. Based on what the investigators know of 24 hour IOPs this drug is expected to work well at night potentially by enhancing uveoscleral outflow. This study will test this hypothesis.
In studies of new glaucoma medications the preferred study population includes ocular hypertensive subjects. These people have high IOP but no optic nerve damage and no glaucoma. They may be taking prescribed IOP lowering drugs for this condition or they may not. Those taking ocular drugs are asked to stop taking them. Since glaucoma drugs affect aqueous humor dynamics in different ways, it is essential that no residual medical effect remains from these drugs. A washout period is necessary to remove all topical ocular drug effects. A concern for patient safety exists when OHT patients are taken off of glaucoma medications, as IOP may rise during the washout period. In order to monitor IOP in these patients, a biweekly check of the IOP is made. If pressure rises above the ophthalmologist's preset "target pressure" at any point, then the patient is removed from the study and returned to his/her previous medical regimen.