PURPOSE: To retrospectively evaluate the safety and efficacy of an Ahmed glaucoma valve (AGV) modified with a polyethylene shell (M4) to reduce the fibrotic reaction around the drainage plate compared with the S2 and FP7 models in patients with glaucoma. METHODS: The medical records of patients who underwent implantation of the AGV FP7, S2, and M4 were reviewed. The primary outcome measure was cumulative probability of success, defined as an intraocular pressure (IOP) between 5 and 18 mm Hg and >20% reduction of IOP without loss of light perception, need for additional IOP-lowering surgical procedures, or removal of AGV. RESULTS: Seventy-six, 38, and 40 eyes received the FP7, S2, and M4 with a mean follow-up time of 578±157, 662±186, and 504±158 days, respectively. The mean IOP was reduced from 31.0±10.6 to 13.9±5.5 mm Hg in the FP7 group, 33.5±12.1 to 15.8±8.1 mm Hg in the S2 group, and 27.0±12.0 to 15.0±4.0 mm Hg in the M4 group at 1 year (P=0.31). At 1 year, the cumulative probability of success was 70%, 66%, and 80% and at 18 months, 61%, 53%, and 52% in the FP7, S2, and M4 groups, respectively (P=0.99). Complications were similar among groups. CONCLUSIONS: No significant difference was observed between the AGV M4, FP7, and S2 at 1 year. Additional follow-up is required to determine its long-term safety profile and efficacy.