Abstract
Purpose: :
Although peripheral prism glasses are reported to assist hemianopic patients with obstacle detection on the blind side, objects are perceived shifted toward the seeing side. Perceiving the obstacle in its veridical direction would facilitate an accurate and timely motor response. Using a custom-designed perceptual-motor training tool we evaluated whether intensive reach-and-touch training with visual feedback could facilitate adaptation to the change in perceived direction.
Methods: :
Five patients with hemianopia (2 with spatial neglect) were fit with high power (40 or 57 diopters) peripheral prism glasses. They completed 1 to 5 training sessions of 90 to 120 minutes each on the computerized touch-screen training tool. While fixating a central cross, they reached out to finger touch stimuli (2° square) presented within the prism expansion areas and the seeing hemifield. Touch position was recorded. As training progressed, stimulus duration decreased and more complex backgrounds were used. Training involved use of feedback from both visual-motor guidance and visible scene-shift context.
Results: :
For stimuli presented in the expansion areas, all patients had high detection rates (>90%). As expected, initial touches were inaccurate by an amount roughly equal to the prism-induced image shift (21° - 29°). With training, 2 patients without neglect were able to touch the real stimulus position. In these patients, touch accuracy error, the distance from the actual stimulus position to the touch position, reduced to only 4° (IQR 2° to 11°) and 3° (IQR 2° to 9°), comparable to (but more variable than) touch accuracy for stimuli presented in the seeing hemifield, 3° (IQR 3° to 4°) and 3° (IQR 2° to 4°), respectively. Two others (1 with neglect, 1 without) touched an intermediate position (7°, IQR 4° to 16° and 10°, IQR 7° to 15°). These patients were aware that the true stimulus position was in the blind field, but were unable to use visual-motor feedback to guide the touch. The 5th patient (with neglect) continued to touch the image-shifted position.
Conclusions: :
These preliminary data suggest that training with visual-motor guidance and scene-shift context may lead to adaptation of perceived direction in some patients learning to use peripheral prism glasses. Further work continues to fine-tune training parameters, increase sample size, record reaction times, and investigate whether direction adaptation leads to improved performance on functional tasks.
Keywords: neuro-ophthalmology: cortical function/rehabilitation • perimetry • low vision