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Tina Yitian Gao, Timothy Ledgeway, Alyssa Lie, Nicola Anstice, Joanna Black, Paul McGraw, Benjamin Thompson; Continuous Flash Suppression in Amblyopia is Asymmetric and Non-selective for Stimulus Orientation. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1521.
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© ARVO (1962-2015); The Authors (2016-present)
Suppression of the amblyopic eye is thought to contribute to visual impairments associated with amblyopia. It is unknown whether suppression in amblyopia is an extreme form of normal interocular suppression or if distinct pathophysiology is involved. To explore this, we examined orientation-tuning of suppression in patients with amblyopia and visually normal controls using a psychophysical technique known as continuous flash suppression (CFS).
Eleven adult controls (mean age 24.1 years, SD 4.9 years) and seven adults with unilateral amblyopia (mean age 27.6 years, SD 5.1 years) participated after providing written informed consent. During the CFS protocol, one eye viewed a test probe (1.8 cycles/degree horizontal sinusoidal grating) that underwent a contrast increment, while the other eye viewed spatially 1-dimensional dynamic noise refreshing at 10 Hz to induce suppression. Orientation offsets between the noise and test probe were varied from 0 degrees (parallel) to 90 degrees (orthogonal) and contrast increment thresholds for the test probe were measured separately for each eye. Half-Gaussian functions were used to characterise orientation-tuning bandwidth.
In controls, distinct orientation-tuning of interocular suppression was present with a mean half-height bandwidth of 32.9 degrees (SD 17.0 degrees). No statistically significant differences were found between dominant and non-dominant eyes for orientation bandwidth (p=0.26) or contrast increment threshold at maximum (p=0.34) or minimum (p=0.83) suppression.For all amblyopic patients, strong suppression of the amblyopic eye by the fellow eye was evident. Five out of seven patients did not exhibit orientation-tuning of suppression and the amblyopic eye was unable to suppress the fellow eye. For the remaining two amblyopic patients, orientation bandwidth was within the range of controls, but suppression in CFS was asymmetric, whereby the amblyopic eye was more strongly suppressed than the fellow eye despite equal monocular sensitivity at the tested spatial frequency. Clinical characteristics were unrelated to whether patients showed tuned or un-tuned suppression.
The majority of patients with amblyopia showed a distinct pattern of interocular suppression compared to controls. The suppression is broadband in orientation and ocular dominance is highly asymmetrical.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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