Trabeculectomy is increasingly being performed earlier in the treatment of primary open-angle glaucoma (POAG). Surgically-induced alterations in corneal curvature resulting from filtering surgery may have a significant impact on patients, especially younger ones, whose vision may already be compromised by visual-field loss. Using data obtained by computer-assisted topographic analysis performed preoperatively and at 12 weeks postoperatively, we longitudinally studied the corneal surface changes induced by primary trabeculectomy in eight eyes undergoing surgery for POAG or normal-tension glaucoma. Additional data collected included refraction, keratometry, axial length, intraocular pressure, and pachometry. Five of eight eyes developed 1.50 to 2.50 diopters of steepening in the 90-degree meridian. One patient developed flattening in the 180-degree meridian without vertical steepening. Two patients had little change in the central optical zone. Of the six eyes with induced with-the-rule astigmatism, keratometry was less sensitive than topographic analysis in detecting the changes induced by trabeculectomy. Our data indicate that changes in corneal curvature are induced by filtering surgery, but may be undetectable without topographic analysis.