Influence of glaucoma surgery on visual function: a clinical cohort study and meta-analysis

Purpose To determine the cost (loss of visual function associated with the procedure) and benefit (long-term preservation of the visual field) of glaucoma surgery. Methods We included 100 patients who underwent glaucoma surgery (Baerveldt glaucoma implant [BGI], n = 61; trabeculectomy [TE], n = 39). Preoperatively, the median (interquartile range [IQR]) standard automated perimetry mean deviation (MD) was -12 (-16 to -6) dB. We analysed the change in visual acuity (BCVA) and MD due to the procedure and, in a subset with at least 5 years of perimetric follow-up both pre- and postoperatively (n = 20), the change in rate of progression (ROP; time rate of change in MD). For the surgery-induced change in ROP, we also performed a meta-analysis including the current and previously published studies. From the surgery-induced decrease in MD and change in ROP, we calculated the average postoperative duration needed for the benefit to surpass the cost. Results Mean (standard deviation) MD decline was 1.3 (2.7) and 1.0 (2.3) dB for BGI (p <0.001) and TE (p = 0.009), respectively; no significant surgery-induced changes in BCVA were found (p = 0.08 and p = 0.12, respectively). In our study, surgery was associated with a non-significant deceleration of ROP (from -0.37 [0.52] to -0.15 [0.48] dB/year; p = 0.23). The meta-analysis, based on eight studies, showed an overall surgery-induced change in ROP of 0.44 (95% confidence interval 0.25 to 0.64; p <0.0001) dB/year. Conclusion Glaucoma surgery significantly reduces the progression velocity in glaucoma. On average, the benefit of glaucoma surgery surpasses the cost after approximately 1.5 years.