IN THE Proctor Lecture of 1951, Duke-Elder1 described three main types of phasic variation of the intraocular tension in simple glaucoma. These were, first, the falling type of curve, occurring in 20% of cases, in which the tension was highest early in the morning; second, the rising type, occurring in 25% of cases, in which the tension was highest in the late afternoon, and, third, the double variation, or biphasic type, occurring in 55% of cases, in which there were two peaks, one in the forenoon and the other in the late afternoon. He noted that simple glaucoma was a state "characterized initially by an instability of the ocular tension which shows a diurnal phasic variation of more than 5.0 mm. Hg."
Grant,2 in 1950, described his technique for tonography in detail and discussed its theory and application. As he stated, his work was based on the calculations
HORWICH H, BREININ GM. PHASIC VARIATIONS IN TONOGRAPHY. AMA Arch Ophthalmol. 1954;51(5):687-694. doi:10.1001/archopht.1954.00920040697013