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Published: Apr 27, 2013 | Updated: Apr 28, 2013
By Charles Bankhead , Staff Writer, MedPage Today
Amblyopia improved significantly after a 2-week dual-eye training session with the popular video game Tetris, investigators reported.
Simultaneous training of both eyes (dichoptic) and monocular training both led to significant improvement in visual acuity compared with baseline, but dichoptic training resulted in significantly greater improvement compared with monocular training (P<0.0001), Robert F. Hess, PhD, DSc, of McGill University in Montreal, and co-authors reported April 26 in Current Biology.
“It has been reported that 40 hours of monocular video game play can improve visual acuity in adults with amblyopia by an average of 1.6 LogMAR, whereas performing other monocular activities has no effect,” the authors said in correspondence to the journal editors.
“Our results demonstrate that effects of the same or large magnitude can be achieved after just 10 hours of dichoptic video game play and that dichoptic training is much more effective than monocular training.”
Amblyopia, or lazy eye, does not respond to conventional interventions involving suppression of one eye, such as by use of a patch. Recent studies have shown that the adult human visual cortex has a substantial amount of plasticity, “suggesting that something must be actively preventing the adult brain from learning to see through the amblyopic eye.”
The “something” might be a signal from the contralateral eye that suppresses cortical inputs from the affected eyes, the authors continued. Existence of a gating mechanism might explain the lack of plasticity seen in the amblyopic eye.
Use of dichoptic stimulation to eliminate suppression of the amblyopic eye might improve plasticity and visual acuity to a greater degree as compared with forced use of the amblyopic eye by itself.
To investigate their hypothesis, Hess and colleagues recruited 18 adults with amblyopia into a randomized comparison of dichoptic versus monocular training involving the video game Tetris. The patients were randomized to daily 1-hour sessions of playing the game monocularly or dichoptically. After 2 weeks (10 sessions), patients in the monocular group crossed over to dichoptic training for an additional 2 weeks.
During dichoptic training standard stimulus elements were presented separately to each eye, and lower-contrast stimuli were also presented to the fixing eye to offset suppression and facilitate binocular combination of the stimuli.
At the end of the first 2-week period, patients in both groups had significant improvement in visual acuity (P<0.0001 for dichoptic, P=0.04 for monocular). Dichoptic learning resulted in greater improvement by a factor of 4 (P<0.0001). After crossover to dichoptic training, the monocular group improved visual acuity by a factor of 4 as compared with the first 2 weeks of the intervention (P<0.0001).
Dichoptic training improved stereopsis (depth perception) by a factor of 4 (P=0.03) whereas monocular training had no effect. The between-group difference in treatment effect reached statistical significance (P=0.01). After crossover to dichoptic training, stereopsis improved significantly in the monocular group (P=0.02).
Additionally, dichoptic training led to a significant reduction in suppression (P<0.0001). Monocular training had no effect on suppression, but after crossover to the dichoptic intervention, significant improvement occurred (P=0.02).
“This strongly suggests that suppression of the amblyopic eye gates plasticity within the adult amblyopic visual cortex,” the authors concluded. “By directly reducing suppression, learning was enabled and significant improvements in both monocular and binocular visual function occurred, although visual function did not recover to normal levels. This provides a basis for the treatment of amblyopia in adults who currently have no treatment options.
Primary source: Current Biology