Tonography has become a recognized test in clinical ophthalmology and the source of much experimental and scientific information. It is simply a method of pushing fluid out of the eye by a given weight in a given time. The problem discussed in this paper is What fluid?—Is it entirely aqueous or partly aqueous and partly blood?
The fact that the application of a tonometer to an eye for a period of time caused the pressure to drop was known to Schiøtz and his early followers. Wegner1 concluded that the drop in tension was primarily due to displacement of blood from the uveal system. Bailliart2 felt that the fall in tension was from the modification of the choroidal vascular system, which allowed itself to be flattened. Subsequent investigators have supplied ample proof that external pressure in the form of tonometry displaces aqueous from the eye, but the role of
BETTMAN JW, FELLOWS V, CHAO P, JOHNSON JP. The Effect of Tonography and Other Pressures on the Intraocular Blood Volume. AMA Arch Ophthalmol. 1958;60(2):230-236. doi:10.1001/archopht.1958.00940080246007