Diurnal variations in outflow facility.

Tonography was carried out at 8 AM, 2 PM, and 8 PM on 43 normal eyes, 58 open-angle glaucomatous eyes and 10 ocular hypertensive eyes. Diurnal variations in outflow facility and their relation to those in intraocular pressure (IOP) were studied. Diurnal variations in outflow facility were present in almost all eyes, with approximately a 10% exception. The average diurnal variation in true outflow facility (deltaCtrue) was 0.10 microliter/min/mm Hg in normal eyes and 0.07 microliter/min/mm Hg in glaucomatous eyes. The average rate of diurnal variation in true outflow facility: formula: (see text) was 43.6% in normal eyes and 69.1% in glaucomatous eyes. The value was greater in glaucomatous eyes than in normal eyes. The curve of diurnal variations in true outflow facility was divided into 5 types, and in glaucomatous eyes the value of outflow facility was apt to increase in the morning and decrease in the evening. In 42% of the normal and 45% of the glaucomatous eyes, inverse relation was seen between diurnal variations in outflow facility and diurnal rhythm in IOP. It is thought that diurnal variations in outflow facility, along with diurnal fluctuations in the rate of aqueous formation, are one of the factors responsible for the diurnal rhythm found in IOP.