Episcleral venous pressure of mouse eye and effect of body position

Abstract

Purpose: To measure the episcleral venous pressure (EVP) of the mouse eye and to investigate the effect of body position on EVP and intraocular pressure (IOP).

Methods: A microneedle connected to a pressure transducer was used to measure IOP in NIH Swiss white mice. To measure EVP, a reservoir connected to this transducer allowed modulation of the intracameral pressure by changing its height. As intracameral pressure was gradually lowered, there was an observable reflux of erythrocytes from an episcleral vein into Schlemm's canal. The IOP at which this occurred was the endpoint of the EVP measurement. EVP and IOP were measured in a horizontal body position (0 degrees ) analogous to an awake mouse and at 30 degrees and 60 degrees head-down body position from the horizontal position. EVP was measured twice in each eye of 6 mice.

Results: Mean IOP at 0 degrees, 30 degrees and 60 degrees of head-down position was 16.5 +/- 0.6, 18.2 +/- 0.6, and 19.5 +/- 1.8 mmHg, respectively. EVP (horizontal) was 9.6 +/- 1.3 mmHg (N = 6 eyes). EVP significantly increased with increasing degree of head-down position (SNK test, p < 0.05). EVP at 30 degrees and 60 degrees of head-down position was 11.2 +/- 1.3 and 13.3 +/- 1.5 mmHg, respectively.

Conclusions: Mouse EVP was successfully measured based on the detection of erythrocyte reflux from an episcleral vein into Schlemm's canal. Both EVP and IOP increased with the degree of the head-down body position.