Consensus on Outcome Measures for Glaucoma Effectiveness Trials: Results From a Delphi and Nominal Group Technique Approaches

PURPOSE: Comparing the relative effectiveness of interventions across glaucoma trials can be problematic due to differences in definitions of outcomes. We sought to identify a key set of clinical outcomes and reach consensus on how best to measure them from the perspective of glaucoma experts.

METHODS: A 2-round electronic Delphi survey was conducted. Round 1 involved 25 items identified from a systematic review. Round 2 was developed based on information gathered in round 1. A 10-point Likert scale was used to quantify importance and consensus of outcomes (7 outcomes) and ways of measuring them (44 measures). Experts were identified through 2 glaucoma societies membership-the UK and Eire Glaucoma Society and the European Glaucoma Society. A Nominal Group Technique (NGT) followed the Delphi process. Results were analyzed using descriptive statistics.

RESULTS: A total of 65 participants completed round 1 out of 320; of whom 56 completed round 2 (86%). Agreement on the importance of outcomes was reached on 48/51 items (94%). Intraocular pressure (IOP), visual field (VF), safety, and anatomic outcomes were classified as highly important. Regarding methods of measurement of IOP, "mean follow-up IOP" using Goldmann applanation tonometry achieved the highest importance, whereas for evaluating VFs "global index mean deviation/defect (MD)" and "rate of VF progression" were the most important. Retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) was identified as highly important. The NGT results reached consensus on "change of IOP (mean of 3 consecutive measurements taken at fixed time of day) from baseline," change of VF-MD values (3 reliable VFs at baseline and follow-up visit) from baseline, and change of RNFL thickness (2 good quality OCT images) from baseline.

CONCLUSIONS: Consensus was reached among glaucoma experts on how best to measure IOP, VF, and anatomic outcomes in glaucoma randomized controlled trials.