PURPOSE: To compare modified viscotrabeculotomy (VCO-Tbo) to modified trabeculotomy (Tbo) in late-onset primary congenital, juvenile open-angle, steroid-induced, and pigmentary glaucoma. METHODS: Patients were randomly assigned to VCO-Tbo and Tbo groups in this study. Intraocular pressure (IOP), antiglaucoma medications, and success/failure rates were assessed. A linear mixed model was used to compare the change trend at different follow-up times. Survival time was evaluated using the Kaplan-Meier graph and Log-Rank test. RESULTS: The mean IOP at 1, 3, and 12 months in the VCO-Tbo group was 14.1 ± 3.1, 15.9 ± 3 and 17 ± 3.1 mmHg, respectively. The mean IOP at the same time points in the Tbo group was 15.9 ± 3.3, 17.6 ± 3.5 and 18.4 ± 3.2 mmHg (P = 0.051, 0.058, 0.088, respectively). The VCO-Tbo group had significantly lower IOP after six months (16.5 ± 4.1 mmHg vs. 18.7 ± 3.8 mmHg
p = 0.031) and by the last visit (16.8 ± 2.1 mmHg vs. 18.8 ± 2 mmHg
p = 0.013). The reduction in the number of medications was significant in both groups compared to baseline (P <
0.001), but there was no significant difference between groups (P = 0.450). The complete and qualified success rate was 43.9% and 34.1% in the VCO-Tbo group and 46.8% and 10.6% in the Tbo group at the final follow-up (p = 0.040, and 0.039, respectively). CONCLUSION: Both procedures are effective in IOP and medication reduction. The survival time and efficacy of modified trabeculotomy can be augmented by injecting cohesive viscoelastic in the Schlemm's canal.