THE EFFECT OF ORAL DEXAMETHASONE ON THE CIRCADIAN-RHYTHM OF AQUEOUS-HUMOR FLOW IN HUMANS

Purpose. To determine if the circadian rhythm of plasma corticosteroid activity is necessary for the circadian rhythm of aqueous humor flow to occur in humans. Methods. Twenty normal volunteers were recruited f or this randomized, double-masked, placebo-controlled study. Oral dexa methasone was given at a dose of 0.5 mg every 6 hours; this is equival ent to more than two times the normal 24-hour endogenous adrenal corti costeroid production. This dosage schedule will maintain a relatively constant level of corticosteroid action throughout a 24-hour period. T opical fluorescein and a scanning fluorophotometer were used to measur e the rate of aqueous humor flow. Subjects were studied on two separat e days. On one study day, the subject took 0.5 mg of dexamethasone eve ry 6 hours; on the other study day, the same subject took a placebo ev ery 6 hours. Results. During the morning, aqueous flow was 4.06 +/- 0. 70 mu l/min (mean +/- SD) in subjects taking dexamethasone and 3.82 +/ - 0.85 in subjects taking a placebo. This 6% higher dexamethasone flow was not significant (P = 0.10). During the afternoon, aqueous flow wa s 3.83 +/- 0.78 in subjects taking dexamethasone and 3.52 +/- 0.77 in subjects taking a placebo. This 9% higher dexamethasone flow was stati stically significant (P = 0.02). The nighttime aqueous flow was 1.38 /- 0.45 in subjects taking dexamethasone and 1.43 +/- 0.34 in subjects taking the placebo. There was not a significant difference between pl acebo and dexamethasone during the night (P = 0.40). On each day, intr aocular pressure was measured at 8:00 AM, 4:00 Phl, and 6:00 AM. When comparing dexamethasone to placebo, no significant difference was obse rved in any of the intraocular pressures. Conclusions. The study is in terpreted as showing that the reduction of aqueous humor flow during s leep can occur in the absence of a comparable fall in plasma corticost eroid activity.