Ultrasound biomicroscopic quantitative analysis of light-dark changes associated with pupillary block

To quantitatively analyze the changes in anterior chamber angle and iris configuration induced by varying illumination in patients with narrow angles and pupillary block.

Twenty-four eyes of 24 patients with pupillary block (mean age, 52.5 years) had ultrasound biomicroscopic images of the angle and iris structures obtained superiorly, nasally, inferiorly, and temporally. Images were performed in the light and the dark. We measured the angle opening distance, iris thickness, iris chord length, iris-lens touch, and iris curvature.

Changes in iris and angle configuration occurred within a few seconds of a change in lighting. The mean dark measurements were statistically significantly less than the mean light measurements for angle opening distance (96 +/- 18 vs 185 +/- 26 microm, P = .0001), iris chord length (2,505 +/- 61 vs 3,001 +/- 69 microm, P = .0001), and iris-lens touch (350 +/- 20 vs 693 +/- 35 microm, P = .0001). The mean dark measurements were statistically significantly greater than the mean light measurements for iris thickness at 500 microm from the scleral spur (367 +/- 10 vs 307 +/- 25 microm, P = .0001), and 1,500 microm from the scleral spur (404 +/- 14 vs 347 +/- 12 microm, P = .0001). Iris curvature in all four quadrants was statistically significantly greater in the dark than the light.

This study quantitatively confirms that angle narrowing in the dark in eyes with pupillary block is associated with iris shortening, increased iris thickness, and increased iris convexity. Iris-lens touch is relatively small in pupillary block and decreases with dilation. Angle narrowing with dilation is not related to increased iris-lens touch and occurs promptly without requiring time for aqueous pressure buildup behind the iris.