Abstract
Purpose :
Glaucoma and cataracts are common comorbidities that can progress to blindness. Studies have shown that cataract extraction alone can reduce IOP, providing benefits for patients with glaucoma.
Minimally invasive glaucoma surgery (MIGS) with cataract surgery has risen in popularity in recent years. MIGS involves implanting microscopic devices to facilitate aqueous outflow. The relative contribution of cataract extraction and MIGS to net IOP reduction is uncertain.
Paired-organ case-control studies obviate heterogeneity and substantially reduce the impact of interindividual variability upon studies of therapeutic efficacy, enhancing statistical power. This retrospective paired-eye study analyzes IOP control over two years in patients who underwent phacoemulsive cataract surgery alone in one eye, and the same surgery combined with Schlemm's canal iStent implantation in their fellow eye. We hypothesize that there will be no statistically significant reduction of IOP with the addition of MIGS to cataract extraction.
Methods :
Retrospective case-control study: 26 patients (17M,9F;73.9y±1.35) underwent bilateral cataract extraction without complication, with concomitant MIGS in only one eye; no change in topical treatment pre- or post-op. Mean ΔIOP from baseline (pre-op) was calculated for each eye 0-2mo, 2-5mo, & 6-18mo post-op using clinically documented IOP measurements. Paired t-test was applied to analyze the significance of the difference between the two paired-eye treatment groups' IOP reduction.
Results :
All eyes were medicated pre-op with baseline mean IOP of 17.4mmHg and 17.8mmHg in cataract extraction and MIGS eyes respectively (n=26). Mean difference in ΔIOP between paired eyes never exceeded 3mmHg, and failed to reach statistical significance at any time interval. Mean IOP reduction in cataract+MIGS eyes never exceeded 13%; standalone cataract surgery reached 12% reduction at the second post-op interval.
Conclusions :
American Academy of Ophthalmology guidelines define minimal clinical efficacy for any glaucoma treatment as >20% IOP reduction. No quantitative evidence of a significant reduction in IOP attributable to iStent was observed among this cohort. Comparable publications in the literature indicate the statistical power of this paired-organ case-control sample to detect a clinically significant effect (or even a clinically trivial but statistically significant effect) should be very high.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.