June 2015
Volume 56, Issue 7
ARVO Annual Meeting Abstract  |   June 2015
The relationship between fusion, suppression, and diplopia in amblyopia
Author Affiliations & Notes
  • Daniel P. Spiegel
    Ophthalmology, McGill University, Montreal, QC, Canada
  • Alex S. Baldwin
    Ophthalmology, McGill University, Montreal, QC, Canada
  • Mark A. Georgeson
    Vision Sciences, Aston University, Birmingham, United Kingdom
  • Reza P Farivar
    Ophthalmology, McGill University, Montreal, QC, Canada
  • Robert F Hess
    Ophthalmology, McGill University, Montreal, QC, Canada
  • Footnotes
    Commercial Relationships Daniel Spiegel, None; Alex Baldwin, None; Mark Georgeson, None; Reza Farivar, None; Robert Hess, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 2196. doi:
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      Daniel P. Spiegel, Alex S. Baldwin, Mark A. Georgeson, Reza P Farivar, Robert F Hess; The relationship between fusion, suppression, and diplopia in amblyopia. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2196.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: Traditionally, it has been thought that no binocular combination occurs in amblyopia. However, there is a growing body of evidence that there are intact binocular mechanisms in amblyopia rendered inactive under normal viewing conditions due to imbalanced monocular inputs. Georgeson and Wallis (2014) recently introduced a novel method to investigate fusion, suppression and diplopia in normal population. We have modified this method to assess binocular interactions in amblyopia.

Methods: Ten amblyopic and ten control subjects viewed briefly-presented (200 ms) pairs of dichoptically separated horizontal Gaussian blurred edges. Subjects reported one central edge, one offset edge, or a double edge as the vertical disparity was manipulated. The experiment was conducted at a range of spatial scales (blur widths of 4, 8, 16, and 32 arc min) and contrasts. Our model, based Georgeson and Wallis (2014), converted subjects’ responses into probabilities of fusion, suppression, and diplopia.

Results: When the normal participants were presented equal contrast to each eye the probability of fusion gradually decreased with increasing disparity, as the probability of diplopia gradually increased. In only a small proportion of the trials, normal participants experienced suppression. The pattern was consistent across all edge blurs. Interestingly, the majority of amblyopes had a comparable pattern of fusion, i.e. decreasing probability with increasing disparity. However, with increasing disparity the amblyopes tended to suppress the amblyopic eye, experiencing diplopia only in a small proportion of trials particularly at large blurs. Increasing the interocular contrast offset favouring the amblyopic eye normalized the pattern of data in a way similar to normal participants. There were some interesting exceptions: strong suppressors for which our contrast range was inadequate and one case in which diplopia dominated.

Conclusions: This task is suitable for assessing binocular interactions in amblyopic participants and providing a way to quantify the relationship between fusion, suppression and diplopia. In agreement with previous studies, our data indicate the presence of binocular mechanisms in amblyopia. A contrast offset favouring the amblyopic eye normalizes the measured binocular interactions in the amblyopic visual system.


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