Association between baseline angle width and induced angle opening following prophylactic laser peripheral iridotomy

Abstract

Purpose: To evaluate the association between baseline angle width and laser peripheral iridotomy (LPI)-induced opening of the anterior chamber angle.

Methods: Anterior segment optical coherence tomography images captured before and after LPI were analyzed to determine the angle opening distance at 250 μm (AOD250), 500 μm (AOD500), and 750 μm (AOD750) from the scleral spur; trabecular-iris space area at 500 μm (TISA500) and 750 μm (TISA750) from the scleral spur; angle recess area at 750 μm (ARA750) from the scleral spur; and trabecular-iris angle (TIA). Differences in preoperative and postoperative measurements for the anterior chamber angle width parameters were compared by paired Student's t-tests. Univariate and linear mixed-effects regression models were used to examine the association between baseline and LPI-induced opening of anterior chamber angle width parameters.

Results: Eighty-four eyes of 52 primary angle closure suspects were included in the analysis. AOD250, AOD500, AOD750, TISA500, TISA750, ARA750, and TIA significantly increased following LPI by paired Student's t-tests (all P < 0.0001). Lower baseline measurements were significantly associated with greater postoperative opening in all anterior chamber angle width parameters in both univariate and linear mixed-effects regression analyses (all P < 0.05).

Conclusions: Our results showed significant opening of the anterior chamber angle width after LPI and demonstrated an inverse association between baseline and LPI-induced opening of the anterior chamber angle width, such that eyes with a more crowded anterior chamber angle undergoing LPI had a greater magnitude of increase in anterior chamber angle width after the procedure.

Keywords: angle opening distance; angle recess area; laser peripheral iridotomy; trabecular–iris angle; trabecular–iris space area.

Figure 1.

An illustration of TISA500 and TISA750. TISA500 was defined as the trapezoidal area with the following boundaries: anteriorly, a perpendicular line between the inner corneoscleral wall and the iris surface at 500 μm anterior to the scleral spur; posteriorly, a line perpendicular to the inner corneoscleral wall extending from the scleral spur to the iris surface; superiorly, the inner corneoscleral wall; and inferiorly, the iris surface. The same method was used for TISA750.

Figure 2.

An illustration of AOD250, AOD500, AOD750, and ARA750. AOD250 was defined as the length of the line extending from the anterior iris to the corneal endothelium, perpendicular to the line drawn along the trabecular meshwork at 250 μm anterior to the scleral spur. The same method was used for AOD500 and AOD750. ARA750 was defined as the area bordered by the anterior iris surface, corneal endothelium, and a line perpendicular to the corneal endothelium that is drawn to the iris surface from a point 750 μm anterior to the scleral spur (shaded area).

Figure 3.

An illustration of TIA. TIA was measured in degrees by using the angle function in the built-in version 3.0 software of the Visante OCT, which defined the iris root as the vertex of the angle with the two sides of the angle formed by extending lines from the vertex to points of standardized length on the posterior surface of the cornea and the anterior surface of the iris.