Simultaneous measurement of intraocular pressure in the anterior chamber and the vitreous cavity.

PURPOSE

To simultaneously measure, using manometry, the changes of intraocular pressure (IOP) in the anterior chamber and in the vitreous cavity of a single porcine eye, induced by an external column of water.

METHODS

We prospectively measured IOP simultaneously in seven freshly enucleated porcine eyes in both the anterior chamber and the vitreous cavity. Measurements were obtained through blood-pressure transducers connected to 21-gauge catheters. A third cannula was inserted into the anterior chamber to increase the IOP; when the cannula was connected to the water column, the pressure increased rapidly from 0 to 180 mmHg. Changes were registered every 5 seconds during the first minute. Statistical analysis was performed using the Wilcoxon signed-rank test. P ≤ 0.05 was considered significant.

RESULTS

Before the IOP was increased, the median basal IOP value was 18 mmHg in the anterior chamber and 23 mmHg in the vitreous cavity (P > 0.05). Sixty seconds after the end of the experiment, the median IOP value was 135 mmHg (range 122-145) in the anterior chamber and 55 mmHg (range 16-68) in the vitreous cavity (P < 0.01).

CONCLUSION

Cannulation of the anterior chamber measures the actual IOP; however, the IOP measured by cannulation in the vitreous cavity using the same catheter diameter was different, possibly because of the viscosity of the vitreous. The viscosity of the vitreous probably makes the cannulation method of IOP evaluation in the vitreous cavity inaccurate.