Ultrasound biomicroscopic findings in humans with shallow anterior chamber and increased intraocular pressure after the prone provocation test.

PURPOSE

To investigate ultrasound biomicroscopic findings in human eyes with shallow anterior chamber and risk of anterior chamber angle-closure glaucoma after the prone provocation test.

METHODS

A total of 32 consecutive patients (64 eyes) with bilateral shallow anterior chamber who were at risk for primary angle-closure glaucoma underwent the prone provocation test in a lit room. Before and immediately after measurement of intraocular pressure in this test, high-frequency ultrasound biomicroscopy was performed in the horizontal and vertical directions, and the chamber angle views were recorded at the 3-, 6-, 9-, and 12-o'clock positions.

RESULTS

Ten eyes of six patients exhibited an increase in intraocular pressure of 8 mm Hg or more, a positive response, with the remainder showing a negative response to the test. In the eyes with a positive response to the test, the profile of the iris showed a markedly convex shape with a large space behind the posterior iris. However, the anterior chamber angle of each eye remained open, even during the high level of intraocular pressure caused by the provocation.

CONCLUSIONS

The present results suggest that no angle closure occurs during the initial increase of intraocular pressure after the prone provocation test. Such an initial increase of intraocular pressure was associated with high pressure in the posterior chamber because of the relative pupillary block. A time lag was observed between the high intraocular pressure caused by the pupillary block and the occurrence of angle closure.