Determination of the pseudofacility by fluorophotometry in the human eye

Pseudofacility (decrease in aqueous humor flow in response to increase in the intraocular pressure (IOP)) has been evaluated in animals and in humans by a combination of different techniques that seriously alter the ocular physiology, such as the cannulation of the eyeballs, use of radioactive isotopes, perilimbic suction cups or tonography. Very different results have been obtained. Our objective is to relate the value of the aqueous humor flow in humans (as measured by fluorometry) with IOP. In order to obtain the widest range of IOP possible, we have performed this study in both normal as well as glaucoma patients.

48 eyes were studied, corresponding to 31 subjects (mean age 58 +/- 14 years). Of these, 21 corresponded to normal subjects and 27 to glaucoma patients. The aqueous humor flow (F) was determined by fluorophotometry (Protocol of Yablonsky) and the IOP was measured thereafter.

The mean value of F was 2.1 +/- 0.5 microliter/min for healthy eyes and 2.2 +/- 0.7 microliter/min for glaucoma-affected eyes. The values were not different (p > 0.1). The mean value of the IOP was 15.3 +/- 3.1 mmHg in the normal population and 22.1 +/- 4.3 mmHg in the glaucoma patients. A linear relationship between F and IOP was found (r = -0.41, p < 0.05, decrease in F = 0.081 microliter min-1 mmHg-1).

The value of the pseudofacility in the humans can be estimated at 0.081 microliter min-1, mmHg-1, which constitutes 27% of the total outflow facility. This figure also makes it possible to estimate the role of the ultrafiltration in blood in the production of the aqueous humor since it is assumed that active secretion is pressure-independent. The results obtained are concordant with a secondary but no unimportant role of the plasmatic ultrafiltration with respect to the active secretion.