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

PURPOSE: To determine corneal biomechanical changes following major glaucoma procedures. METHODS: 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 ≥580 microns or ≤500 microns, post-operative intraocular pressure (IOP) > 21 mmHg or ≤ 5 mmHg, and any surgical complication were excluded. Main outcome measures included changes in corneal hysteresis (CH) and corneal resistance factor (CRF). RESULTS: 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). CONCLUSION: 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.