The authors describe a randomised double masked study of 29 participants with ocular hypertension (OHT) who either self-administered 0.2% brimonidine or placebo three times daily for six weeks. Patients were seen during day time and night time visits and had measurements of aqueous flow, outflow facility, episcleral venous pressure and seated and supine IOP. Uveoscleral outflow was calculated mathematically. The authors found that the effect of brimonidine was partially dependent on both the body position of the subject during IOP measurement and the time between the last dose. They concluded that in patients with OHT brimonidine treatment for six weeks significantly reduced seated IOP during the day, however, the study had several limitations due to techniques available such as for aqueous humour dynamics and calculation uveoscleral outflow.