Evaluation of the Pressure cup Technique for the Measurement of Aqueous Humor Formation

¹ Wilmer Institute, Johns Hopkins University Medical School Baltimore, Md.

An evaluation of two types of pressure cups to measure the rate of formation of aqueous humor in normal eyes of human subjects has been made. The application of sufficient negative pressure to the pressure cups placed on freshly enucleated eyes has been found to cause a complete closure of the drainage vessels. Hoivever, the vessels could be. reopened by increasing the intraocular pressure. The pressure cup technique was applied to normal eyes of human subjects for 15 minutes and the results agreed closely with those reported by Ericson.² Prolonged periods of observation on individual eyes indicated that the intraocular pressure increased to a new steady state well beloio the blood pressure. The coefficient of the outflow facility toas determined before and after pressure cup studies to determine whether the cup caused a prolonged occlusion of the drainage vessels. A significant reduction in the outflow facility was found immediately after removal of the cup from the eye, but no difference was found 30 minutes later at ivhich time the intraocular pressure had returned to normal. The use and limitations of the pressure cup technique to study the formation of the aqueous humor in normal eyes are discussed in the light of the present study. It is concluded that the rate of outflow of aqueous humor may be largely, if not completely, prevented by the application of a negative pressure of 50 mm. Hg to the pressure cup provided the intraocular pressure does not exceed 30 mm. Hg. The experimental evidence indicates that above this pressure leakage of aqueous humor can occur.