To evaluate the safety and efficacy of phacoemulsification as a first line treatment of acute angle closure glaucoma (AACG) and to evaluate the preoperative and postoperative anterior chamber angle width and anterior chamber parameters using anterior segment OCT(AS-OCT) and Pentacam. Sohag University Hospital, Sohag city, Egypt. Prospective comparative interventional case series study. Patients presented with AACG. After control of high intraocular pressure (IOP), all participants were scheduled for phacoemulsification within a week after the attack. Preoperative and postoperative angle width, anterior chamber volume and anterior chamber depth was measured by AS-OCT and Pentacam to evaluate angle changes. Fifty eyes with AACG were enrolled in the study. The mean IOP was lowered significantly from 40.23 ± 10.4 mmHg preoperatively to 11.4 ± 3.3 mmHg 3 months after surgery. The mean preoperative temporal angle widened from 18.13 ± 3.65 degree to 36.16 ± 4.46 3 months after phacoemulsification. Also, the mean preoperative nasal angle widened from 17.80 ± 3.45 preoperatively to 36.18 ± 4.47 3-month postoperative. The mean preoperative AC volume was 49.4 ± 5.73 μL. After surgery the AC volume increased significantly to 138.2 ± 29.78 μL. The mean preoperative ACD was 1.58 ± 0.12 mm that deepened significantly after surgery to 3.19 ± 0.43 mm. Early phacoemulsification is very effective in treatment of AACG cases immediately after medical control of high IOP and resolution of corneal oedema. This was proved by imaging and measuring the angle width, anterior chamber volume and anterior chamber depth using AS- OCT and Pentacam.