Corneal Biomechanical Changes Following Trabeculectomy, Phaco-trabeculectomy, Ahmed Glaucoma Valve Implantation and Phacoemulsification

To determine corneal biomechanical changes following major glaucoma procedures. In a prospective comparative case series, corneal biomechanical properties were assessed using the Ocular Response Analyzer (ORA, Reichert Inc., Depew, New York, USA) before and 3 months after surgery in 89 eyes of 89 patients undergoing trabeculectomy + mitomycin C (MMC) (23 eyes, group 1), phacotrabeculectomy + MMC (23 eyes; group 2), Ahmed glaucoma valve (AGV) implantation (17 eyes; group 3) or phacoemulsification (PE) alone (26 non-glaucomatous eyes; group 4). Patients with history of contact lens use, previous intraocular surgery, any chronic corneal disease, central corneal thickness equal or more than 580 microns or equal or less than 500 microns, post-operative intraocular pressure (IOP) more than 21 mmHg or equal or less than 5 mmHg, and any surgical complication were excluded. Main outcome measures included changes in corneal hysteresis (CH) and corneal resistance factor (CRF). Preoperatively, CH was lower in glaucomatous versus non-glaucomatous eyes (5.4, 5.3, 5.2 and 8.1 mmHg in groups 1, 2, 3 and 4 respectively, p < 0.001). Three months after surgery, mean CH increased by 2.16, 2.29 and 2.30 mmHg in groups 1, 2 and 3 respectively (P < 0.001) but only by 0.11 mmHg in group 4 (p = 0.704). The postoperative increase in CH in glaucomatous eyes was more significant when IOP was reduced by more than 10 mmHg. CRF also showed a significant increase in all study groups postoperatively (P < 0.001). CH and CRF increased significantly 3 months after glaucoma procedures. Alterations in corneal biomechanical properties should be considered when measuring IOP after successful glaucoma surgery.