Comparison of intraocular pressure and anterior segment parameters in subjects with asymmetrical primary angle closure disease

Background: To compare intraocular pressure (IOP) and anterior segment parameters between eyes with unilateral primary angle closure glaucoma (PACG) and their fellow eyes with primary angle closure (PAC) or primary angle closure suspect (PACS). Methods: Subjects underwent anterior segment imaging using 360-degree swept-source optical coherence tomography (SS-OCT, CASIA Tomey, Nagoya, Japan) and ocular investigations including gonioscopy and IOP measurement. Each SS-OCT scan (divided into 8 frames, 22.5 degrees apart) was analysed and an average was obtained for the following anterior segment parameters: iridotrabecular contact (ITC), angle opening distance (AOD750), iris thickness and curvature, anterior chamber width, depth and area (ACW, ACD and ACA) and lens vault (LV). Results: Among 132 unilateral PACG subjects (mean age: 62.91 +/- 7.2 years; 59.1% male), eyes with PACG had significantly higher presenting IOP (24.81 +/- 0.94 vs. 18.43 +/- 0.57 mmHg, p < 0.001), smaller gonioscopic Shaffer grade (2.07 +/- 0.07 vs. 2.31 +/- 0.07, p < 0.001) and a greater extent of peripheral anterior synechiae (PAS, 1.21 +/- 0.21 vs. 0.54 +/- 0.16 clock hours, p = 0.001). PACG eyes also exhibited increased ITC, ITC area, greater LV and smaller AOD750, ACD and ACA (all p < 0.05). Using the forward stepwise regression model, an increase in 1 mmHg in presenting IOP before laser peripheral iridotomy (LPI) increases the odds of having PACG by 9% (95% confidence interval 5%-14%). Conclusions: PACG eyes have higher presenting IOP, smaller anterior segment parameters, greater extent of PAS, and larger LV compared to their fellow eyes with angle closure. Narrower anterior chamber dimensions and higher presenting IOP before LPI may increase risk of chronic elevated IOP and glaucomatous optic neuropathy after LPI.