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B. T. Barrett, G. K. Panesar, I. E. Pacey, A. J. Scally; Suppression in the Central Visual Field Is Not a Common Feature in Amblyopia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2591. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopes are generally assumed to suppress at least part of the image from the affected eye. However, the nature of the relationship between amblyopia and suppression has proved difficult to characterise. Here we investigate, using a novel experimental approach, the prevalence and extent of amblyopic-eye suppression in a simple detection task.
Blue-on-yellow sensitivity was determined along the horizontal meridian (25 degrees either side of a fixation mark). 4 viewing conditions were used: yellow filter before the fellow or amblyopic eye & translucent occluder before the fellow or amblyopic eye. The blue stimulus was invisible through the yellow filter and this enabled the sensitivity of each eye to be determined in non-rivalrous, minimally-dissociated conditions when the eyes are in their habitual motor position. Thirteen amblyopes participated (11 with strabismus). Results were analysed using a simple linear regression model repeated for each individual to compare the sensitivity of each eye under the yellow-filter and translucent-occluder conditions (STATA 9.2).
The table shows how monocular sensitivities in the amblyopic and fellow eyes were affected by switching from the yellow-filter over the untested eye (i.e. where the untested eye was open and permitted to view all except the blue stimulus) to the translucent occluder. Suppression was considered to exist when sensitivity across a substantial region of the horizontal meridian was reduced in the yellow-filter condition relative to the translucent-occluder condition. Amblyopic-eye suppression was evident in only 4 cases (30%); surprisingly, suppression of the fellow eye by the amblyopic eye was evident in 2 cases (15%). There was no relationship between the presence/absence of suppression and the depth of amblyopia.
Our results suggest that suppression is not a common feature of amblyopic vision. On the contrary, the monocular sensitivity of the amblyopic eye is more likely to be unchanged, or even enhanced, in habitual viewing conditions.
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