A unified rule for binocular contrast summation applies to normal vision and common eye diseases

Ying Zi Xiong, Rong Liu, Mi Young Kwon, Ava K. Bittner, Cynthia Owsley, Gordon E. Legge

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

PURPOSE. Binocular summation refers to better visual performance with two eyes than with one eye. Little is known about the mechanism underlying binocular contrast summation in patients with common eye diseases who often exhibit binocularly asymmetric vision loss and structural changes along the visual pathway. Here we asked whether the mechanism of binocular contrast summation remains preserved in eye disease. METHODS. This study included 1035 subjects with normal ocular health, cataract, agerelated macular degeneration, glaucoma, and retinitis pigmentosa. Monocular and binocular contrast sensitivity were measured by the Pelli-Robson contrast sensitivity chart. Interocular ratio (IOR) was quantified as the ratio between the poorer and better eye contrast sensitivity. Binocular summation ratio (BSR) was quantified as the ratio between binocular and better eye contrast sensitivity. RESULTS. All groups showed statistically significant binocular summation, with the BSR ranging from 1.25 [1.20, 1.30] in the glaucoma group to 1.31 [1.27, 1.36] in the normal vision group. There was no significant group difference in the BSR, after accounting for IOR. By fitting a binocular summation model Binocular = (Leftm + Rightm)1/m to the contrast sensitivity data, we found that the same binocular summation rule, reflected by the parameter m, applies across the five groups. CONCLUSIONS. Cortical binocular contrast summation appears to be preserved in spite of eye diseases that can affect the two eyes differently. This finding supports the importance of assessing both monocular and binocular functions, rather than relying on a monocular assessment in the better eye as a potentially inaccurate surrogate measure.

Original languageEnglish (US)
Article number2777971
JournalInvestigative Ophthalmology and Visual Science
Volume62
Issue number13
DOIs
StatePublished - Oct 2021

Bibliographical note

Funding Information:
Supported by grants from the National Institutes of Health (R01 EY002934 to GEL; R01 EY027857 to MK; NIH R01EY18966 to CO; 1K99EY030145-01A1 to Y-ZX; K23 EY018356 and P30 NR008995 to AKB), by grants from the National Institute on Aging (P50 AG11684 and P30AG22838 to CO); by a Research to Prevent Blindness/Lions Clubs International Foundation low vision research award (to MK) and by the Foundation Fighting Blindness. MK and CO’s work was also supported by an unrestricted grant from Research to Prevent Blindness, Inc. to the Department of Ophthalmology and Visual Sciences at UAB and a grant from the EyeSight Foundation of Alabama to UAB. AKB’s work was also supported by an unrestricted grant from Research to Prevent Blindness, Inc. to the Department of Ophthalmology at UCLA. Y-ZX was also supported by a fellowship from Envision Research Institute during the preparation of the paper.

Publisher Copyright:
© 2021 The Authors.

Keywords

  • Binocular summation
  • Contrast sensitivity
  • Eye diseases
  • Normal vision

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