Anterior Segment Optical Coherence Tomography in Evaluation of Impact of Laser Peripheral Iridotomy on Anterior Segment Morphology and IOP in Primary Angle Closure Spectrum Patients: A Quasi-experimental Study

Introduction: A leading cause of bilateral blindness worldwide, Primary Angle Closure Glaucoma (PACG) is estimated to affect 16 to 20 million people, with an estimated four million bilaterally blind. Laser Peripheral Iridotomy (LPI) is the primary treatment for angle closure based on its ability to relieve pupillary block. After LPI in eyes with narrow angles, progression to angleclosure glaucoma is uncommon, even in high-risk eyes such as the fellow eyes of patients with a unilateral acute angleclosure attack. Gonioscopy is limited in its ability to accurately characterise Anterior Chamber (AC) morphology. Anterior Segment Optical Coherence Tomography (AS-OCT), however, has emerged as a method for obtaining objective, reproducible high-resolution images that allow for quantification of AC parameters. Aim: The present study was aimed to evaluate, by AS-OCT, the changes in the AC angle width parameters following N:d YAG LPI in patients with Primary Angle Closure (PAC) spectrum patients and to study the Intraocular Pressure (IOP) changes following N:d YAG LPI in patients with PAC Spectrum (PACS) patients. Materials and Methods: The present quasi-experimental study was done in the Ophthalmology Department at SRM Medical College Hospital and Research Centre, Katthankulathur, Chennai, Tamil Nadu, India. Forty eyes were included in the study, this includes Best-Corrected Snellen Visual Acuity (BCVA), Slit-lamp evaluation including Van Herick’s Grading of angle and Lens status, Goldmann Applanation Tonometry, Corneal Pachymetry (CCT), undilated fundoscopy, gonioscopy and anterior segment OCT were performed at baseline. Tonometry and gonioscopy were performed on first week follow-up visit. While repeat AS-OCT was performed at one month follow-up visit. Changes in mean values between baseline (Pre LPI) and post LPI visits were assessed using statistical methods such as paired student’s t-test and Chi-square test. The p-value less than 0.05 were considered statistically significant. Results: The mean IOP prior to LPI was 22.33 mmHg, which reduced to 16.95 mmHg Following LPI (p<0.001). Mean CCT was 536.675 um, with minimum being 500 um and maximum being 560 um. AC angle parameters on AS-OCT, i.e.,- Trabecular-Iris Angle (TIA), AOD 500, AOD 750, TISA 500, TISA 750, Scleral Spur Angle (SSA), Anterior Chamber Width (ACW) and Anterior Chamber Area (ACA), all increased significantly following LPI (p<0.001 for all parameters). Thus, demonstrating widening of AC angle and flattening of the convex Iris configuration following LPI. Central AC depth had insignificant but minimal change following LPI (p>0.05) Conclusion: LPI is efficacious in widening of the AC angle in eyes with PACS disease in the short term. AS-OCT as an imaging modality has several advantages that make it an excellent tool for large-scale screening of PACG.