Effect of phacoemulsification on intraocular pressure and bleb function in eyes with previous trabeculectomy

AIM: To observe the intraocular pressure (IOP) control and bleb function after phacoemulsification in patients with previous history of successful/qualified success mitomycin-C augmented trabeculectomy.METHODS: This was a retrospective cohort study. Data of patients who had undergone trabeculectomy with subsequent cataract surgery were extracted from server. All patients had previous either success/qualified success trabeculectomy done. They went through uncomplicated phacoemulsification via clear corneal incision. Postoperative follow-up, review of bleb and IOP readings using Goldmann tonometer were taken. Details that were investigated include postoperative IOP control, visual improvement, number of anti-glaucoma medications, as well as the timing from trabeculectomy to phacoemulsification. Comparison with control group was made.RESULTS: Fifteen eyes from thirteen patients fulfilled the criteria for study and had undergone uncomplicated phacoemulsification between January 2014 to June 2016 on a post-trabeculectomy eye. Two of the eyes had secondary glaucoma while the other thirteen had primary glaucoma. All phacoemulsifications were done at least 6mo after trabeculectomy (mean 14.7±4.3mo). There was only 1 eye (6.7%) requiring anti-glaucoma medications before the cataract surgery. This number increased to 4 (26.7%) at 1-year post phacoemulsification. The number further increased to eight (53.3%) at 2y post-phacoemulsification. The number of anti-glaucoma drops needed after surgery at 2y ranged from 2-4. In all the 15 eyes, there was no statistically significant change in IOP control between pre-cataract surgery (mean 13.4±2.9 mm Hg) compared to 1y (mean 14.1±3.2 mm Hg, P=0.357) and 2y (mean 15.1±3.3 mm Hg, P=0.212) post phacoemulsification. Visual improvement after phacoemulsification however is significant, from a preoperative average visual acuity of logMAR 1.52±1.00 to a postoperative average visual acuity of 0.53±0.54 (P=0.000, paired t-test).CONCLUSION: This analysis shows significant visual improvement following cataract surgery in post-trabeculectomy patients without compromising IOP control. However, a reduced bleb function is noted following the surgery evidenced by the increase in number of anti-glaucoma drops used after surgery especially two years after the cataract surgery. Patients should be counselled regarding the possibility of restarting on anti-glaucoma medications post-phacoemulsification. The timing and sequence of cataract and glaucoma surgery should be optimized for best outcome.