Hemianopia patients confirm prism benefits

By Lynda Williams, Senior medwireNews Reporter

Results from a crossover trial confirm anecdotal reports that patients with homonymous hemianopia (HH) benefit from wearing peripheral prism glasses.

Trial participants were 5.3 times more likely to state a preference to continue wearing horizontal 57-prism diopter glasses designed to expand the lateral field by up to 30° than to continue wearing sham glasses (5-prism diopter), the study shows.

Specifically, 64% of the 61 patients who completed the trial said they would like to continue with the treatment after 4 weeks of wearing the real prism glasses, compared with just 36% after 4 weeks of wearing the sham glasses.

“Peripheral prism glasses provide a simple and inexpensive mobility rehabilitation intervention for hemianopia,” say Alex Bowers (Schepens Eye Research Institute, Boston, Massachusetts, USA) and co-authors.

The researchers note that patients who preferred the real prism glasses reported experiencing much better obstacle avoidance and visual comfort than with the sham glasses, and found them more helpful when walking.

By contrast, participants who preferred the sham glasses said obstacle avoidance and visual comfort were only slightly better than with the real prism glasses. The main reasons given for their preference were finding the sham pair more visually comfortable and having less difficulty using them than real prism glasses, rather than better functional performance.

The researchers say that double-blind use of placebo prism glasses is important to account for these preferences. “These are patients who in an open-label trial might artificially inflate success rates when only a short-term follow-up is included (eg, 1 month) because they would like to continue with the study intervention but for the wrong reasons and would likely discontinue use of the device before a longer term follow-up (eg, 6 months),” explain Bowers et al.

Both glasses resulted in a trend toward improvement in the patients’ overall mobility scores from baseline but this did not reach significance. However, among the patients who continued to wear prism glasses of their preference for 6 months, mobility scores significantly improved only in those given the real version.

“[T]his study addresses the lack of controlled trials identified in recent systematic reviews of interventions for homonymous visual field loss and strengthens the evidence base for the efficacy of peripheral prism glasses as a mobility aid for patients with HH,” the team concludes in JAMA Ophthalmology.

“The next step should be a clinical trial with outcome measures evaluating functional performance on real-world or simulated mobility tasks.”

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