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The prevalence of suppression in amblyopic individuals
Author(s) -
Barrett Brendan,
Panesar Eve,
Pacey Ian
Publication year - 2008
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.2007.00530_15.x
Subject(s) - meridian (astronomy) , strabismus , visual field , optometry , ophthalmology , fixation (population genetics) , ocular dominance , medicine , foveal , audiology , optics , psychology , retinal , physics , population , visual cortex , environmental health , astronomy , neuroscience
Purpose: A popular view of visual functioning in individuals with amblyopia is that the weaker eye is suppressed in key regions of the binocular visual field. Indeed, some have argued that chronic interocular suppression may represent the cause of amblyopia. Here we evaluate the prevalence of amblyopic‐eye suppression in a simple light detection task when the eyes are open, minimally dissociated and in their habitual motor position. Methods: A custom program on the Humphrey Field Analyzer (Carl Zeiss Meditec Inc., Dublin, CA, USA) was used to measure detection thresholds for a blue light on a yellow background along the horizontal meridian at two‐degree intervals to an eccentricity of 25 degrees on either side of the fixation mark. The fellow eye was prevented from seeing the target using three different methods: (1) full‐occlusion (i.e. no light entered the fellow eye), (2) a translucent occluder (3) a yellow filter in front of the fellow eye. In (3), the yellow filter only prevented the fellow eye from seeing the blue stimulus; the fixation mark and the background remained visible (minimal‐dissociation condition). Fourteen amblyopes participated in the study, of whom 11 had strabismus. Results: Three basic patterns of results were observed. (1) Only three of the fourteen participants (∼21%) showed evidence of suppression, where amblyopic‐eye sensitivity was lower with the fellow eye open. In these cases, the retinal locations that showed greatest suppression corresponded to the direction and angle of the strabismus. (2) Three participants (∼21%) showed the opposite effect to the result in (1); i.e. amblyopic‐eye sensitivity was greatest when the fellow was open with minimal dissociation between the eyes. One possible explanation is that the dominance of the fellow eye caused this reduction. (3) Seven participants (50%) exhibited patterns of amblyopic sensitivity that did not depend upon the occlusion status of the fellow eye. The results for one participant did not fit into any of the above patterns. Conclusions: Suppression appears not to be a universal feature of central amblyopic vision. Our results for this simple detection task suggest that suppression may exist in as few as 20% of amblyopes. These results present a challenge to the view that suppression represents a root cause of amblyopia but they are consistent with the view that the amblyopic eye makes a useful contribution under habitual viewing conditions.