Size Matters for Interplicata Diameter: A Case-Control Study of Plateau Iris

Abstract

Purpose: Ultrasound biomicroscopy (UBM) has been used to characterize anterior segment dimensions in plateau iris configuration (PIC), but transverse measurements between the recesses of the ciliary sulcus (sulcus-to-sulcus diameter [STSD]) and the ciliary body processes (interplicata diameter [IPD]) have not been reported. We measured STSD and IPD and compared these among eyes with PIC, primary angle closure (PAC), and control eyes with open angles.

Design: Retrospective, cross-sectional clinical study.

Participants: Sixty-nine participants, 37 PIC, 13 PAC, and 19 controls.

Methods: We searched our clinical UBM database for PAC and PIC cases. Controls were assembled by reviewing images obtained for surveillance of ocular surface lesions. Anterior segment measurements were performed using the UBM digital caliper tool. Robust-fit ANOVA identified among-group differences. Pairwise t tests were used to test the significance of between-group differences.

Main outcome measures: Anterior chamber depth (ACD), angle opening distance (AOD), ciliary body area and thickness, iris area, horizontal and vertical STSD, and horizontal and vertical IPD.

Results: Fifty-five left eyes were analyzed (30 PIC, 10 PAC, and 15 controls). ACD was smaller in PAC than in PIC and control eyes (P < 0.05 for PIC vs. PAC; P < 0.01 for control vs. PAC). Mean AOD was smaller in PIC than controls (P < 0.05) and smaller in PAC than PIC (P < 0.001). Vertical STSD was smaller in both PAC and PIC than controls (P = 0.04 for PIC vs. control; P < 0.01 for PAC vs. control). Horizontal STSD was smaller in PIC than controls (P = 0.02). Vertical IPD was smaller in PIC than controls (P = 0.04) and smaller in PAC than PIC eyes (P = 0.02). Horizontal IPD was smaller in PIC and PAC than controls (P = 0.03 for PIC vs. control; P < 0.01 for PAC vs. control).

Conclusions: STSD and IPD are narrower in PIC and PAC than in healthy eyes. Further studies that examine the ratio of white-to-white cornea diameter to the IPD may provide a mechanism for reported cases of in-the-bag uveitis-glaucoma-hyphema syndrome in PIC.