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  • Addiction, Drugs
  • Information from Lay-Language Summaries is Embargoed Until the Conclusion of the Scientific Presentation

    823—Striate Cortex: Ocular Dominance Plasticity

    Wednesday, November 13, 2013, 1:00 pm - 5:00 pm

    823.16: Patching the eye makes it stronger: Enhanced binocular vision following brief monocular deprivation

    Location: Halls B-H

    1McGill, Montreal, QC, Canada; 2Ophthalmology, McGill Univ., Montreal, QC, Canada; 3Ophthalmology, McGill Univertsity, Montreal, QC, Canada; 4Optometry and Vision Sci., Univ. of Auckland, Auckland, New Zealand

    Abstract Body: Recent evidence has shown that the adult visual system is plastic enough that even short durations of intensive training can be effective in changing monocular sensitivity. However, here we show that even passive manipulations such as monocular patching can change binocular sensitivity by enhancing the patched eye’s contribution to the binocular percept.
    In this study, the effect of three patching methods on binocular vision were quantified by a binocular phase combination task in normal adults_transparent patching (with light but no pattern), black patching (no light, no pattern) and light patching (with enhanced light but no pattern). We found that, even though the magnitude and the time-course of the patching effect varied across participants and patching methods, short-term (2.5hrs) monocular occlusion strengthened the patched eye’s contribution to binocular vision in all conditions. Immediately after the removal of patch, the patched eye’s contribution to binocular vision increased. This effect reduced with time, returning to baseline at around 30 minutes after the removal of the patch. We found that contrast sensitivity was reciprocally reduced in the unpatched eye, suggesting the effect is driven by cortical binocular interactions.
    Since amblyopia is a developmental disorder in which binocular vision is disrupted, we also investigated whether this reverse form of occlusion (opposite to that commonly used in therapy) might be effective in restoring binocular function. Instead of patching the sighted eye (current therapy), we patched the amblyopic eye and demonstrated that such a procedure has the effect of strengthening the contribution of the amblyopic eye to binocular vision. The strengthening effect was more sustained in adult amblyopes than in normal adults, lasting for at least 60 minutes after the removal of patch in some adult amblyopes.
    These results that suggest that a short duration of monocular patching significantly strengthens the patched eye’s contribution to binocular vision in both the normal and amblyopic visual system have potential theoretical and therapeutic implications.

    Lay Language Summary: Amblyopia or “lazy eye” is the commonest cause (incidence 3%) of unilateral
    blindness in the adult population. It develops in childhood due to unequal stimulation of the two eyes during early visual development. It is currently treated by patching the good eye for 3-­‐8 hrs a day for from 6 months to 2 years. This is effective in some but not all cases and even then the effect may only be partial. Any benefit is at a huge cost in terms of effort by parents and child and psychological side-­‐effects for the child. Unfortunately, the two eyes often don’t end up working
    together and more often than not there is no 3D vision. In fact, in the long-­‐run , after patching therapy has ceased, the vision in the amblyopic eye may reduce, due to suppression by the fellow sighted eye. This treatment approach is not effective in adults (beyond 18 yrs) for whom there is no current treatment option.
    Recently, we have developed a completely new approach, one that focuses on the restoration of binocular function as a first step and we have done this using a novel dichoptic (different images to each eye) video-­‐game approach on a hand-­‐held ipod. The results have been encouraging in that in over half the cases stereopsis can be improved as can the vision in the amblyopic eye. This also happens in a matter of weeks of video-­‐game play (1 hr a day) with none of the side-­‐effects of the previous patching therapy. Furthermore, we have shown that this is just as effective in adults, offering a practical treatment approach for adults for the first time.
    The success of this new approach, which could potentially revolutionize the clinical
    management of amblyopia, points to the binocular aspect of this visual disorder being of prime importance. In the present study we show another method of improving binocular function which is applicable to adults. Here we show that patching an eye for a period of about 2 hrs can result in a strengthening of that eye’s contribution to binocular vision in adults with normal vision. While the effect is short lived, it has implication for cortical plasticity in adults in general and for restoration of binocular function in particular. We also show that , in adults with amblyopia, patching the amblyopic eye for the same period leads to a more sustained strengthening of that eye’s contribution to binocular vision, just as it does
    in adults with normal binocular vision. The implication of this is that short-­‐term patching of the amblyopic eye would help strengthen binocular vision in amblyopes, the foundation of the new treatment approach. This is the opposite of the current patching therapy where the fellow sighted eye is patched, suggesting that the current therapy may be working actively against a positive binocular outcome.
    Short-­‐term patching combined with dichoptic video-­‐game play may be an even more effective way of reversing the visual loss that adults have acquired as the result of a disrupted visual development in childhood.