Optic disc and visual field changes after trabeculectomy

Abstract

Purpose: To assess the changes in optic nerve head (ONH) structure and visual field (VF) sensitivity over time in a cohort of patients with glaucoma after trabeculectomy.

Methods: The MoreFlow Medical Research Council 5-Fluorouracil (5-FU) study was an 80-month prospective randomized controlled trial of per-operative 5-FU versus placebo on the outcomes of primary trabeculectomy. Before surgery, patients had ONH imaging with a retinal tomograph and full-threshold visual field testing. After surgery, ONH imaging was performed annually and VF testing at 4-month intervals. This analysis included only patients with a minimum of 3 years' postoperative ONH and VF data. ONH images were analyzed by linear regression of sector rim area (RA) over time with change defined as a significant slope >1% of baseline RA per year in any sector. VFs were analyzed with point-wise linear regression analysis (PLRA) techniques with the stringent three-omitting criteria used. Eyes were classed as progressing or not based on analysis with either technique. Patients' median IOP level, intervisit IOP fluctuation, and percentage reduction in IOP over the follow-up period were also determined.

Results: Two hundred fifty eyes of 250 patients were suitable for analysis. Of these, 70 (28%) eyes were deemed to show glaucoma progression approximately 5 years after surgery: 20 eyes by ONH alone, 35 by VF alone, and 15 by both methods. Of the 15 shown to be progressing by both ONH and VF analysis, only 7 (3% total cohort) showed congruity in the location of change. Eyes showing changes in both ONH and VF sensitivity had slightly higher median follow-up IOP (median IOP [interquartile range; IQR] nonprogressors 14.0 mm Hg [11.8-16.0 mm Hg], progressors 15.1 mm Hg [12.7-17.0 mm Hg]; Mann-Whitney U test [MWU]; P = 0.03) and lower degrees of IOP reduction from baseline (percentage IOP reduction [IQR]: nonprogressors -38.4% [-51.8% to -26.4%]; progressors -31.4% [-43.1% to -21.5%]; MWU P = 0.01) compared with eyes showing no progression.

Conclusions: The study demonstrates that approximately one third of eyes continued to show progression of glaucoma at five years after trabeculectomy, as determined by trend-based analysis of ONH structural changes and VF sensitivity over time. The study suggests that the degree of IOP reduction after trabeculectomy may play an important role in the progression of glaucoma as detected by both functional and structural methods.