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A systematic review on electronic vision prostheses suggest several improvements on methodology in order to show benefit

A research study, conducted in the Department of Mechanical Engineering and School of Optometry and Vision Science at the University of Auckland, New Zealand, has reported a “need for high-quality evidence of efficacy of retinal implantation to treat RP”.  The systematic review study, on electronic vision prostheses, was focused on electrode array devices that may be implanted surgically, either epi-retinally (at the vitreoretinal interface), sub-retinally (between the photoreceptor layer and choroid), or suprachoroidally. An array may then be coupled to an imaging light sensor device, such as a head-mounted camera, through a wired, or wireless interface. While there has been significant academic and commercial research work in progress, this study was aimed to collect relevant clinical outcomes and data from two independent reviewers, and reporting no conflicts-of-interest (Transl Vis Sci Technol. 2021;10(10):8,


The researchers collected >400 articles and reviewed the full text of 34 articles, based on Cochrane Library methodology. According to the reviewers, results from the studies were “to be at high risk of bias owing to the study design or experimental conduct. Regarding design, studies lacked the measures that typical clinical trials take to protect against bias (e.g., control groups and masking). Regarding experimental conduct, outcome measures were rarely comparable before and after implantation, and psychophysical methods were prone to bias (subjective, not forced choice, methods)”. In addition, the researchers commented that the most common comparison found was between post implantation visual function with the device “powered off versus on”, and this comparison was at high risk of bias.  The search for the systematic review covered journal articles published between January 1, 2015 and October 11, 2019, including the review of seven devices: three were epiretinal, two were subretinal, and two were suprachoroidal.  The high risks of bias reported several reasons, including that: clinical trials were uncontrolled, neither participants nor outcome assessors were masked to the experimental variables, and there were differences between the pre-implantation and post-implantation outcomes assessments.


Commenting on the study, researchers concluded that: “[i]n most discovered studies, neither participants nor assessors were masked to experimental conditions, and control groups were not used as comparators. In clinical trials, outcome assessment was rarely comparable before and after implantation. For these reasons, all discovered studies were judged to be at high risk of bias. Our findings signal an urgent need for the development of objective protocols for vision assessment to be used at multiple sessions both before and after implantation”.  In brief, the researchers pointed out that while the absence of evidence is not evidence of absence, at least in the context of conventional clinical tests, we cannot conclude “no benefit”.  Consequently, the jury must remain out, at least until there is clear independent evidence-based medicine outcomes to show benefit and clinical significance.