Narrowing of the anterior chamber angle during Valsalva maneuver: a possible mechanism for angle closure.

PURPOSE To evaluate changes at the anterior chamber angle during Valsalva maneuver in eyes suspected to have a primary adult glaucoma. METHODS Seventy-six consecutive patients underwent recording of applanation tonometry, measurement of the anterior chamber angle recess, angle opening distance, angle recess area, scleral spur-iris root distance, iris thickness, iridociliary angle, ciliary body thickness, anterior chamber depth, and pupil size on ultrasound biomicroscopy before and during the Valsalva maneuver. The Valsalva maneuver was standardized to a pressure of 40 mmHg for 15 seconds, using a manometer. RESULTS The mean baseline intraocular pressure changed from 19.5+/-4.1 mmHg to 29.5+/-4.8 mmHg during Valsalva (p<0.0001). The anterior chamber angle recess narrowed from 17.9+/-9.5 to 7.8+/-9.2 degrees (p=0.0001). The angle recess area diminished from 0.15+/-0.14 mm2 to 0.14+/-0.12 mm2 (p=0.03) and the scleral spur to iris distance decreased from 0.19+/-0.2 mm to 0.16+/-0.18 mm (p=0.0001). The iridociliary angle narrowed from 72.6+/-33.5 degrees to 62.5+/-32.8 degrees (p=0.04). There was a significant increase in the thickness of the ciliary body, from 0.99+/-0.19 mm to 1.12+/-0.16 mm (p=0.001) and in iris thickness from 0.47+/-0.07 mm to 0.55+/-0.09 mm (p=0.0001). There was no significant change in the angle opening distance, anterior chamber depth, or pupillary diameter. A significant narrowing of the angle to less than 5 degrees was seen in 37 eyes, with iridocorneal apposition present in 28 eyes. After multivariate regression analysis it was found that the baseline ciliary body thickness and angle recess were significant predictors of narrowing of the angle (R2=96.1%). CONCLUSIONS Significant elevation of the intraocular pressure, narrowing of the anterior chamber angle recess, thickening of the ciliary body, and increase in the iris thickness is seen during the Valsalva maneuver. The Valsalva maneuver may lead to angle closure in eyes anatomically predisposed to primary angle closure glaucoma.