Comparison Of Biometric And Anterior Segment Parameters In Subjects With Asymmetrical Primary Angle Closure Disease

To compare ocular biometric and anterior segment parameters between the ‘worse eye’ and contralateral ‘better’ eye in subjects with asymmetrical primary angle closure disease (PACD).

Asymmetrical PACD was defined as subjects diagnosed with primary angle closure glaucoma (PACG) in one eye (the "worse" eye), and either primary angle closure (PAC) or primary angle closure suspect (PACS) in the contralateral eye (the "better" eye). 132 subjects with asymmetrical PACD were recruited. 

Each subject underwent 360 degrees swept-source optical coherence tomography (CASIA Tomey, Nagoya, Japan) imaging, gonioscopy and A-scan ultrasonography. Each 360-degree scan was divided into 8 frames, 22.5 degrees apart, and each frame was analysed to obtain these anterior segment parameters: iridotrabecular contact (ITC), angle opening distance (AOD750); iris thickness and curvature; anterior chamber depth, width, and area (ACW, ACD and ACA); lens vault (LV); anterior vault (AV, computed as ACD+LV); and pupil diameter (PD). For each parameter, the average of the 8 frames were computed. Mean differences in ocular biometric and anterior segment parameters were assessed using linear mixed model adjusting for pupil diameter, age and gender.

10 out of 132 subjects (7.6%) with poor quality scans were excluded. The mean age was 65.3 years with 51 (41.8%) females. The worse eyes had significantly higher presenting intraocular pressure (IOP, 24.8 vs 18.4; p<0.001), narrower gonioscopic angles (mean Shaffer grade, p<0.001), greater extent of peripheral anterior synechiae (PAS, p<0.001), greater ITC (p=0.008) and LV (p=0.02), and smaller AOD750 (p=0.005), ACD (p=0.02), and ACA (p=0.02). There were no significant differences (p>0.05) for axial length, lens thickness, iris thickness and curvature, and AV between the worse and better eyes. Presenting IOP correlated negatively with mean Shaffer grade (r=-0.31, p<0.001), AOD750 (r=-0.16; p=0.01), and positively with PAS (r=0.42; p<0.001).

‘Worse’ eyes in subjects with asymmetric PACD are characterized by narrower anterior chamber angles, smaller anterior segment dimensions and large LV. Narrower angles and greater extent of PAS may lead to greater predisposition towards development of elevated IOP. In patients with asymmetric PACD and such biometric differences, earlier follow-up or intervention might be prudent.