Effect of phacoemulsification cataract surgery on intraocular pressure in early glaucoma: A prospective multi-site study

Importance Cataract and primary open-angle glaucoma (POAG) commonly co-exist, and cataract surgery is thought to reduce intraocular pressure (IOP), the major modifiable risk factor of POAG. Background Previous studies exploring the effect of cataract surgery on IOP are limited by retrospective design, lack of a control group, medication use and washout and loss to follow up. Design Prospective, multicentre, matched case-control Australian study. Participants 171 eyes of 108 POAG patients who underwent cataract surgery, matched to 171 control eyes. Methods Serial longitudinal IOP measurements were compared before and after cataract surgery, and relative to the controls. A mixed-effect model was used for the longitudinal data. Main Outcome Measures Change in IOP. Results The mean follow-up time was 4.8 (1.4) years. Cataract surgery reduced mean IOP by 2.22 mmHg (95% confidence interval: 1.93-2.52 mmHg, P < .001) with 59 eyes (34%) achieving at least 3 mmHg reduction. Compared to matched controls, the mean reduction in IOP was 1.75 mmHg (95% confidence interval 1.15-2.33 mmHg; P < .001). Higher preoperative IOP and being on fewer topical glaucoma medications preoperatively were strongly predictive of a larger IOP reduction in a multivariable model. Anterior chamber depth was not associated with IOP reduction. Eyes with preoperative IOP >= 24 mmHg had a mean IOP reduction of 4.03 mmHg with 81% experiencing at least 3 mmHg reduction. Sub-analysis of medication naive and pseudoexfoliation patients showed similar results. Conclusions and Relevance Cataract surgery has a confirmed effect in reducing IOP in a "real world" setting of early glaucoma patients.