Stereopsis & Amblopia: A Mini-review
Thanks to Dr. Dom Maino for his summary of the paper:
Levi, DM. Stereopsis & Amblopia: A Mini-review. Vision Research. 2015
This paper by Levi and colleagues challenges two assumptions that have persisted in the medical literature for the past 2 centuries. The first is that the principal deficit in amblyopia is reduced visual acuity in the affected eye so that the optimal treatment is occlusion of the non-amblyopic eye. However, current research suggests that amblyopia results from poor binocular cooperation between the two eyes, leading, not only to reduced visual acuity in the affected eye, but also to reduced or absent stereopsis. Accordingly, the authors reviewed the impact of amblyopia on stereopsis and the consequences of reduced or absent stereopsis on visuomotor skills, career opportunities, and self-image. Occlusion therapy, even if it results in enhanced visual acuity in the amblyopic eye, produces only modest improvements in stereopsis.
Treatment for amblyopia has traditionally been applied only to children because it was generally assumed that the visual system is malleable only during a critical period in early childhood. However, as the authors point out, a large degree of plasticity in the very young brain does not imply that plasticity comes to an end after childhood. Indeed, the authors review 21 experimental treatments involving 259 individuals, mostly adults. These studies involved monocular and dichoptic perceptual learning protocols, monocular and dichoptic videogame play, and direct stereo training. Across all treatments, 55% of anisometropic amblyopes and 26% of strabismic amblyopes showed substantial improvement in stereoacuity after training, with the dichoptic and direct stereo training protocols proving the most effective.
In summary, Levi and colleagues provide evidence that amblyopia can be treated in adulthood. Limited recovery from amblyopia to date may result from the narrow scope of treatments standardly available and an overly pessimistic view of adult visual plasticity.
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