Manometric measurement of the outflow facility in the living human eye and its dependence on intraocular pressure.

Acta ophthalmologica

PubMedID: 25645503

Karyotakis NG, Ginis HS, Dastiridou AI, Tsilimbaris MK, Pallikaris IG. Manometric measurement of the outflow facility in the living human eye and its dependence on intraocular pressure. Acta Ophthalmol. 2015;.
PURPOSE
The intraocular pressure (IOP) is determined by a dynamic equilibrium between the production and outflow of the aqueous humour. The relationship between IOP and the outflow rate through the conventional and unconventional pathway is quantified by the outflow facility coefficient (C). The purpose of this study is to employ a direct (manometric) tonographic technique and determine C as well as its inverse, resistance (R), as a function of IOP in the living human eye.

METHODS
Nineteen cataract patients were enrolled in the study. An intraoperative manometric device was used to measure IOP. After cannulation of the anterior chamber, the IOP was increased by infusion of controlled amounts of saline solution. At 40 mmHg, the infusion stopped, and a pressure sensor recorded the IOP. The measured pressure-volume relationship was considered in order to convert pressure changes to corresponding ocular volume changes. An appropriate mathematical model was applied to calculate C and (its inverse), R.

RESULTS
The average C was 0.0672 ± 0.0296 µl/min/mmHg at 40 mmHg and 0.2652 ± 0.1164 µl/min/mmHg at 20 mmHg. There was a strong dependence of coefficient C on IOP in all subjects (p < 0.001). The corresponding values for R were 17.9 ± 11.17 min mmHg/µl at 40 mmHg and 4.51 ± 2.69 min mmHg/µl at 20 mmHg.

CONCLUSION
This study provides measurement of outflow facility and its dependence with pressure in healthy living human eyes. This relation is shown to be non-linear, using a direct manometric method.