We compare the short- and mid-term postoperative outcomes of the iStent inject® with its successor, the iStent inject® W. A retrospective monocentric study was performed to compare the iStent inject® used for cataract surgery with the iStent inject® W, also used for cataract surgery. The primary study endpoint was intraocular pressure (IOP) reduction six months after surgery. Six-month follow-up results were available for 35 eyes from 27 patients in the iStent inject® group and for 32 eyes from 25 patients in the iStent inject® W group. IOP reduction at six months post surgery was significantly greater in the iStent inject® W group (−2.2 mmHg [iStent inject® W] vs. −0.06 mmHg [iStent inject®], p = 0.037). There was a statistically greater decrease in glaucoma medication administration at six months in the iStent inject® group than in the iStent inject® W group (−1.28 agents vs. −0.62 agents, p = 0.007). These findings support the hypothesis that the superior positioning of the iStent inject® W (due to its larger base diameter) compared to the iStent Inject® leads to greater IOP reduction. Because of the short follow-up period, small study cohort, and differences in the number of glaucoma patients, the study results must be interpreted carefully.