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Binocular summation of contrast remains intact in strabismic amblyopia

Binocular summation of contrast remains intact in strabismic amblyopia
Binocular summation of contrast remains intact in strabismic amblyopia
PURPOSE. Strabismic amblyopia is typically associated with several visual deficits, including loss of contrast sensitivity in the amblyopic eye and abnormal binocular vision. Binocular summation ratios (BSRs) are usually assessed by comparing contrast sensitivity for binocular stimuli (sensBIN) with that measured in the good eye alone (sensGOOD), giving BSR = sensBIN/sensGOOD. This calculation provides an operational index of clinical binocular function, but does not assess whether neuronal mechanisms for binocular summation of contrast remain intact. This study was conducted to investigate this question.
METHODS. Horizontal sine-wave gratings were used as stimuli (3 or 9 cyc/deg; 200 ms), and the conventional method of assessment (above) was compared with one in which the contrast in the amblyopic eye was adjusted (normalized) to equate monocular sensitivities.
RESULTS. In nine strabismic amblyopes (mean age, 32 years), the results confirmed that the BSR was close to unity when the conventional method was used (little or no binocular advantage), but increased to approximately squareroot2 or higher when the normalization method was used. The results were similar to those for normal control subjects (n = 3; mean age, 38 years) and were consistent with the physiological summation of contrast between the eyes. When the normal observers performed the experiments with a neutral-density (ND) filter in front of one eye, their performance was similar to that of the amblyopes in both methods of assessment.
CONCLUSIONS. The results indicate that strabismic amblyopes have mechanisms for binocular summation of contrast and that the amblyopic deficits of binocularity can be simulated with an ND filter. The implications of these results for best clinical practice are discussed.
contrast sensitivity, strabismus, psychophysics, human, amblyopia
0146-0404
5332-5338
Baker, Daniel H.
92545fbf-bb42-4155-a530-91b917648047
Meese, Tim S.
0c8c57a5-1341-42d6-be91-cac46c6d6f34
Mansouri, Behzad
a0e61c6b-fade-4f7a-9142-524b02c3f4cd
Hess, Robert F.
e68cedd8-a5a6-4ece-aade-c017b1fb1d21
Baker, Daniel H.
92545fbf-bb42-4155-a530-91b917648047
Meese, Tim S.
0c8c57a5-1341-42d6-be91-cac46c6d6f34
Mansouri, Behzad
a0e61c6b-fade-4f7a-9142-524b02c3f4cd
Hess, Robert F.
e68cedd8-a5a6-4ece-aade-c017b1fb1d21

Baker, Daniel H., Meese, Tim S., Mansouri, Behzad and Hess, Robert F. (2007) Binocular summation of contrast remains intact in strabismic amblyopia. Investigative Ophthalmology & Visual Science, 48 (11), 5332-5338. (doi:10.1167/iovs.07-0194).

Record type: Article

Abstract

PURPOSE. Strabismic amblyopia is typically associated with several visual deficits, including loss of contrast sensitivity in the amblyopic eye and abnormal binocular vision. Binocular summation ratios (BSRs) are usually assessed by comparing contrast sensitivity for binocular stimuli (sensBIN) with that measured in the good eye alone (sensGOOD), giving BSR = sensBIN/sensGOOD. This calculation provides an operational index of clinical binocular function, but does not assess whether neuronal mechanisms for binocular summation of contrast remain intact. This study was conducted to investigate this question.
METHODS. Horizontal sine-wave gratings were used as stimuli (3 or 9 cyc/deg; 200 ms), and the conventional method of assessment (above) was compared with one in which the contrast in the amblyopic eye was adjusted (normalized) to equate monocular sensitivities.
RESULTS. In nine strabismic amblyopes (mean age, 32 years), the results confirmed that the BSR was close to unity when the conventional method was used (little or no binocular advantage), but increased to approximately squareroot2 or higher when the normalization method was used. The results were similar to those for normal control subjects (n = 3; mean age, 38 years) and were consistent with the physiological summation of contrast between the eyes. When the normal observers performed the experiments with a neutral-density (ND) filter in front of one eye, their performance was similar to that of the amblyopes in both methods of assessment.
CONCLUSIONS. The results indicate that strabismic amblyopes have mechanisms for binocular summation of contrast and that the amblyopic deficits of binocularity can be simulated with an ND filter. The implications of these results for best clinical practice are discussed.

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Published date: 25 October 2007
Keywords: contrast sensitivity, strabismus, psychophysics, human, amblyopia
Organisations: Cognition

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Local EPrints ID: 49281
URI: https://eprints.soton.ac.uk/id/eprint/49281
ISSN: 0146-0404
PURE UUID: 730019e1-1d67-4b3b-801d-3e0c49248c32

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Date deposited: 26 Oct 2007
Last modified: 13 Mar 2019 20:54

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Contributors

Author: Daniel H. Baker
Author: Tim S. Meese
Author: Behzad Mansouri
Author: Robert F. Hess

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