Hypothesis
Weekly transcorneal electrical stimulation would slow visual field loss in retinitis pigmentosa over a year, as an earlier exploratory study suggested.
What failed
In 52 patients randomized to sham, 150% or 200% of individual phosphene threshold and treated for 52 consecutive weeks, the primary outcome, visual field area, showed only a non-significant trend towards preservation in the 200% arm (p = 0.24); apart from light-adapted single-flash b-wave amplitudes, the other measures did not reach significance, and dry eye symptoms occurred in 31 of 52 patients.
Broken assumption
Electrically stimulating the degenerating retina preserves measurable visual field.
Why
The authors do not explain the primary-outcome null, resting their case for potential benefit on the electroretinography changes and on demonstrated safety and tolerability.
From the published paper: Schatz et al. Investigative Ophthalmology & Visual Science, 2017. ↗CC BY