Researchers of a randomized clinical trial published in November investigated the effectiveness of visual perceptual training to improve field deficits in patients with stroke-related homonymous hemianopia (HH), but were unable to establish significant improvement in the treatment cohort compared with controls. However, they uncovered an unexpected finding regarding fluctuations in visual field changes — important because the standard of care for patients with HH typically involves no intervention, as improvement in deficit fields is believed to be unlikely.
“However, here we found that the visual fields were far from stable, though no clear trend of improvement or worsening could be established given the study intervention and variability in changes,” the research says. “This suggests that patients with HH should be more closely monitored than current standard of care suggests, in order to detect potential changes or fluctuations in visual ability over time.”
In the trial, 48 patients with HH caused by a visual cortex lesion were recruited at 3 sites; University of Rochester Flaum Eye Institute, the University of Miami Bascom Palmer Eye Institute, and the University of Pennsylvania Scheie Eye Institute. Participants were between 21 years and 75 years old and exhibited no ocular disease. The patients were randomized into intervention and control groups, and trained in motion discrimination tasks — exercises which, in previous non-randomized laboratory work, appeared to be a potential therapy for reducing field deficits. The intervention group performed the discrimination tasks targeted to cortically blind fields, while the control group trained their sighted visual fields.
The fine direction discrimination tasks were practiced on a laptop in an at-home program for 20 to 30 minutes a day, 5 days a week for 6 months, with the goal of 120 days of training. Clinical testing was performed before and after the training and included Humphrey visual fields,, macular integrity assessment (MAIA) for microperimetry, motion discrimination measurement, optical coherence tomography, and a visual quality-of-life survey. The primary outcome for the trial was change in perimetric mean deviation (PMD) in both eyes, measured with the Humphrey field analyzer.
“Following training, although there was some improvement in PMD in both eyes in the deficit-field training group (mean change OD 0.58 dB, 95% CI 0.07, 1.08; mean change OS 0.84 dB, 95% CI 0.22, 1.47), there were no group differences detected in mean change,” the study shows. Further, there appeared no intervention effect on visual field deficit size. Deficit-field trained participants did not report visual quality-of-life improvement or worsening; however, sighted-field trained patients indicated general vision and mental health benefits, which investigators theorize occurred due to positive affirmation during training.
Researchers suggest that outcomes may have been influenced by comparing the intervention group with a sighted-hemifield trained group, and not with an untrained cohort. Also, the psychophysical training tasks took place in a real-world setting which necessitated less hands-on assistance. In addition, since Humphrey visual field analysis and MAIA only assess luminance detection, other tests may have found additional beneficial results related to contrast sensitivity and object recognition.
Further, the overall study population exhibited significantly reduced ganglion cell, inner plexiform layer thickness in both eyes. Investigators propose this finding verifies possible retrograde degeneration in patients with hemianopia. They conclude that early intervention may be best, while visual inputs are still somewhat intact after a stroke; “it remains possible that a training intervention could slow the progression of retrograde degeneration.”
Cavanaugh MR, Blanchard LM, McDermott M, Lam BL, Tamhankar M, Feldon SE. Efficacy of visual retraining in the hemianopic field after stroke: results of a randomized clinical trial. Ophthalmol. Published online November 22, 2020. doi:10.1016/j.ophtha.2020.11.020.