Circadian Rhythms of Plasma Corticoid Levels, Intraocular Pressure and Aqueous Outflow Facility in Normal and Glaucomatous Eyes *

The mean intra-ocular pressure (IOP) for normal eyes is 15 mm.Hg.and this pressure is'the result of a balanced inflow and outflow of aqueous humor.Aqueous inflow is the result of a secretion from the ciliary body.The flow passes between the lens and the iris, through the pupil into the anterior chamber, and then it is removed from the eye through a trabecular network in the angle, and so into the canal of Schlemm.Exit channels from the canal carry the aqueous humor into the episcleral venules on the outside of the eyeball a little posterior to the corneal margin.The control of inflow and outflow is not perfect, and there are variations in pressure, partly haphazard, but largely with a regular circadian rhythm.The pressure tends to be at its lowest in the late evening and early morning.Later in the morning it rises, reaching its maximum, usually between 8:OO A.M. and noon.If IOP has a circadian rhythm, then one must assume that there is also a circadian rhythm of aqueous inflow and aqueous outflow. Aqueous InflowAttempts to investigate the dynamics of aqueous inflow in living human eyes are fraught with difficulty because any instrumental interference tends to alter the status quo.Researchers have had to be dependent upon indirect measurements validated incompletely by direct measurements on living animal eyes and dead human eyes.Ericson' of Sweden, using an indirect method, found that aqueous inflow levels in normal eyes are three times higher by day than by night.Plasma corticoid levels are also higher by day than by night.? The possibility of an interrelationship between plasma corticoids and aqueous inflow prompted Linner,3 in 1959, to instill prednisolone locally in one eye of normal subjects.He found that aqueous inflow was significantly raised in the treated eyes in comparison with the untreated control eyes.He therefore suggested that there is a connection between the function of the adrenal cortex and the rate of aqueous flow.Ericson's and Linner's findings suggested to us that the conditions which occur in the glaucomatous eye might provide an opportunity to investigate further the relationship between plasma corticoids and aqueous *This investigation was financed by giants from the Special Services Committee of the University of Alberta Hospital, the Medical Research Council NO.M.A. 753, the John and Mary R.