ObjectivesThis study quantifies the effect of trabeculectomy on the rate of progression (RoP) of visual field (VF) damage utilising pre- and post-operative visual function as the outcome instead of surrogate outcomes of success.MethodsClinical and VF data from 199 sequential patients who underwent trabeculectomy between 2015 and 2016 were extracted from the network of sites of Moorfields Eye Hospital NHS Foundation Trust. Of these, we analysed 80 eyes of 74 patients who met our inclusion criteria of at least three reliable VFs before and after surgery (false positive rate <15%). The change in mean RoP (dB/year) was tested using point-wise sensitivity values through a mixed effect model with random effects on both intercepts and slopes. A broken-stick regression of sensitivity over time, with a breakpoint at the day of surgery, modelled the individual change in RoP.ResultsWe analysed 10 [9,12] VFs per subject (Median [Interquartile Range]). At surgery, the age was 67 [57, 72] years, mean deviation was −10.84 [−14.7, −5.6] dB and the IOP was 18 [15, 20] mmHg. One year after surgery, the IOP was 10 [8,13] mmHg (p= 0.002). Mean RoP before surgery was −0.94 [−1.20, −0.69] dB/year (Mean [95% credible intervals]) and it was slowed down by 0.62 [0.26, 0.97] dB/year (p< 0.001) after surgery.ConclusionsTrabeculectomy leads to a significant reduction in the RoP of VF loss postoperatively.