Different modes of intraocular pressure reduction after three different nonfiltering surgeries and trabeculectomy

To study the mode of intraocular pressure (IOP) reduction based on correlation with the preoperative IOP after filtering and nonfiltering surgeries. Pre- and postsurgical IOPs at 6 months were compared in one eye of each of 789 subjects with primary open-angle glaucoma, pseudoexfoliation glaucoma, or ocular hypertension who underwent trabeculectomy with adjunctive mitomycin C alone (Lectomy-MMC) (n = 145), phaco-viscocanalostomy (Phaco-VCS) (n = 320), phaco-trabeculotomy ab externo (Phaco-lotomy) (n = 116), or phacoemulsification aspiration and intraocular lens implantation alone (PEA+IOL) (n = 208). The correlation between the preoperative and 6-month postoperative IOP was not significant in eyes that underwent Lectomy MMC (r = −0.026, P = 0.7552, IOP reduction 51.9%), but was significant in eyes treated by Phaco-VCS (r = 0.409; IOP reduction, 24.8%) or PEA+IOL alone (r = 0.294; IOP reduction, 9.9%), and was marginal in eyes treated by Phaco-lotomy (P = 0.062; r = 0.174; IOP reduction, 24.1%). Among the four cohorts studied, the variation in the 6-month postoperative IOP was the largest after Lectomy-MMC. After glaucoma surgery, there are two modes of IOP reduction. The postoperative IOP after Lectomy MMC did not correlate with the preoperative IOP, whereas the postoperative IOP levels after Phaco-VCS, Phaco-Lotomy, and PEA+IOL correlated with preoperative IOP levels. We may be able to predict postsurgical IOP after nonfiltering surgery.