September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
The impact of spherical defocus on diplopia and vergence
Author Affiliations & Notes
  • Clara Mestre
    Indiana University School of Optometry, Bloomington, IN, United States
  • Sonisha Neupane
    Indiana University School of Optometry, Bloomington, IN, United States
  • Deborah Giaschi
    Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, Canada
  • Laurie M. Wilcox
    Centre for Vision Research, York University, Toronto, Canada
  • T. Rowan Candy
    Indiana University School of Optometry, Bloomington, IN, United States
  • Footnotes
    Acknowledgements  NEI: R01 EY014460 (TRC), P30 EY019008
Journal of Vision September 2021, Vol.21, 2802. doi:
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      Clara Mestre, Sonisha Neupane, Deborah Giaschi, Laurie M. Wilcox, T. Rowan Candy; The impact of spherical defocus on diplopia and vergence. Journal of Vision 2021;21(9):2802. doi:

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

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Children with anisometropia (unequal refractive error in the two eyes) are at risk of atypical binocular development. To assess the potential impact of anisometropia on eye movements and perception, we compared the effects of unilateral vs. bilateral spherical defocus on reflexive vergence and perception of single vision. Adults (N=9, 15-51 yrs) and typically developing children (N=4, 7-10 yrs) viewed a dichoptic cartoon (2deg x 3deg) displayed on a grey background. A step change in disparity ranging from 0 to 8deg was introduced for 320ms, followed by a blank screen. Vergence responses were recorded with an Eyelink 1000 and subjects reported whether they perceived the target to be single or diplopic. Spherical defocus ranging from 0.5 to 4D was applied to one or both eyes’ stimuli using convolution of the Point Spread Function for the subject’s pupil size. Six repetitions were presented in random order. Open loop vergence amplitude, at the end of the second latency period, was used to estimate the response (without feedback). The diplopia threshold was defined as the 63% point on a Weibull function fit to the perceptual data. On average across all participants, in the absence of defocus, open loop vergence peaked at +/-1.25deg disparity with amplitudes of 0.33±0.24deg convergence and -0.41±0.25deg divergence. For adults, bilateral defocus had no effect on this reflex portion of the response, as 4D of defocus resulted in 0.28±0.42deg and -0.40±0.30deg amplitudes. Unilateral defocus of 4D reduced amplitudes to 0.14±0.28 and -0.25±0.20deg. The mean adult diplopia threshold increased significantly from 1.28±0.51deg with no defocus to 1.71±0.62deg when 4D bilateral defocus was applied, but decreased to 0.89±0.27deg when the 4D defocus was unilateral. Reflex vergence responses were made to all of these small central stimuli. In adults, although bilateral defocus appeared protective against diplopia, anisometropia tended to disrupt both vergence and perception.


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