PurposeTo assess the IOP-lowering effect of adding a mattress suture (Ahmed’s suture) to non-penetrating deep sclerectomy (NPDS), in patients with open angle glaucoma over a 12-month follow-up period.MethodsThis is a randomized controlled study comparing 52 eyes with a sub-flap Ahmed’s suture modified NPDS (group A) and 51 with a conventional NPDS (group B). Success of surgery was categorized as complete success if the IOP remained between 6 and 18 mmHg without medications and as qualified if topical medications were required.ResultsThe post-operative IOP at the 1st week, 3rd, 6th, 9th & 12th months follow ups in group A were significantly lower (7.3 ± 2.1, 12.0 ± 2.3, 12.6 ± 2.7, 13.6 ± 3.4 & 13.8 ± 3.8 mmHg) than in B (9.2 ± 1.9, 14.0 ± 3.1, 14.8 ± 2.9, 15.4 ± 2.6 & 15.7 ± 2.7 mmHg) (p= 0.001,p= 0.001,p= 0.002,p= 0.027 &p= 0.029 respectively). The percentage of IOP reduction after 1 year was significantly higher in group A than in group B (49% vs. 36.5%). At the end of the 12-month follow-up, 81% of group A and 69% of group B were considered as complete success. Multivariate regression analysis showed lower 1st week post-operative IOP was associated with better outcome.ConclusionIn conclusion, the Ahmed’s suture, a simple, novel and economic modification, maintains lower IOP levels and has a higher success rate over conventional DS, as it is 30% more effective in reducing the IOP.