Improving the Feasibility of Glaucoma Clinical Trials Using Trend-Based Visual Field Progression Endpoints

Abstract

Purpose: There have been concerns that short-term clinical trials for evaluating new treatments in glaucoma would require prohibitively large sample sizes when using visual field endpoints, given that glaucoma is often a slowly progressive disease. This study sought to determine the required sample size for such trials using event-based analyses, and whether it can be reduced using trend-based analyses.

Design: Longitudinal, observational study.

Participants: 321 eyes of 240 glaucoma participants followed under routine clinical care using 242 visual field for an average of 10 years.

Methods: Sample size requirements were derived using computer simulations that reconstructed "real-world" visual fields by combining estimates of point-wise variability according to different threshold levels and rates of change obtained from the clinical glaucoma cohort. A clinical trial lasting 2 years with testing every 3 months was simulated, assuming that the new treatment halted visual field change in various percentages of participants (or "responders"). Treatment efficacy was evaluated by: (a) Difference in incidence of point-wise event-based progression (similar to the commercially available Guided Progression Analysis), and (b) Difference in rate of visual field mean deviation (MD) change between groups using linear mixed models (LMMs).

Main outcome measures: Sample size to detect a statistically significance difference between groups.

Results: Between-group trend-based analyses using LMMs reduced sample size requirements by 85-90% across the range of new treatment effects when compared to the conventional point-wise event-based analysis. To detect the effect of a new treatment that halted progression in 30% of the participants under routine clinical care (equal to a 30% reduction in average rate of MD change) with 90% power, for example, 1924 participants would be required per group using event-based analysis, but only 277 participants per group if LMMs were used.

Conclusions: The feasibility of future glaucoma clinical trials can be substantially improved by evaluating differences in the rate of visual field change between groups.

Keywords: Visual fields; clinical trials; glaucoma; sample size.

Figure 1:

Plot of the power to detect a 30% treatment effect against sample size per group for survival analysis of event-based progression (grey line) versus trend analysis of rates of mean deviation change using linear mixed models (black line).