Using Friedenwald's tonometric tables, Grant was able to measure the resistance* to outflow of aqueous humor in 1950. This new clinical method was conventionally referred to as tonography. It has acquired considerable practical importance in investigating the hydrodynamics of the aqueous humor.
One of the criticisms that may be leveled at tonography is the use of Friedenwald's coefficient of ocular rigidity.
According to the formula published by Grant, in 1950, the resistance to outflow can be calculated by means of the equation
R=the resistance to outflow of aqueous humor
Pt1=the initial tonometric pressure, i. e., the pressure prevalent in the eye due to the weight of the tonometer at the beginning of tonography
Pt2=the tonometric pressure at completion of tonography
K=the coefficient of ocular rigidity according to Friedenwald
Vc1=the volume of the corneal indentation at the beginning of tonography
PRIJOT E. Tonography Under Constant Distention of the Sclera. AMA Arch Ophthalmol. 1959;61(4):536-540. doi:10.1001/archopht.1959.00940090538006