This is a single-centre randomised controlled trial of 875 patients with bilateral primary angle closure suspect (PACS) who received YAG laser iridotomy (LPI) prophylactic treatment in one eye randomly and the fellow eye served as control over 72 months. Central corneal endothelial cell density (ECD) and morphology were measured using non-contact specular microscopy at baseline, 6, 18, 36, 54 and 72 months postoperatively. The mean age was 59.3 years and 83.5% female. The ECD declined significantly over time (p<0.001) in both treated and control eyes, but the treated eyes showed more progressive cell loss with increasing time (p=0.001). The difference in ECD loss between treated and control eyes was not significant at each follow-up interval until 72 months. Mean cell areas increased significantly over time in both treated and control groups (p<0.001) but no longitudinal change for hexagonality was observed. The limitations of this study included no ECD count at peripheral cornea, therefore focal damage and differences may have been missed, and corneal thickness was not assessed during follow-up period. The authors concluded that ECD decreases over time due to ageing effect primarily and YAG LPI does not appear to cause corneal endothelial damage over the 72 months period clinically.