Suppression scotomas in primary microstrabismus ? a perimetric artefact

Abstract

Static perimetry with stereoscopic targets, "stereo-perimetry", was performed on eight patients with primary microstrabismus to find out how strabismic subjects see under natural conditions, i.e. how they ordinarily make use of their squinting eye. In all cases, suppression scotomas were detectable using dissociating perimetric techniques. By means of stereoperimetry, however, the scotomas were not detectable. On the contrary, stereo-acuity was always best in the center of the suppression scotomas. This result indicates that suppression scotomas of the microstrabismic subjects examined here represented perimetric artefacts. In microstrabismic patients, the cooperation of the deviated eye in the central visual field is probably much better than has previously been thought.

The Regional Extent of Suppression: Strabismics Versus Nonstrabismics

“…Our first question related to whether suppression in strabismic amblyopia took the form of localized scotomata in regions of the amblyopic eye visual field corresponding to the foveal representation of the fixing eye. Contrary to the results of Mehdorn 18 and Barrett, 19 we found evidence of suppression in all the strabismic amblyopes we tested. Contrary also to the earlier results of Travers, 13 Jampolosky, 11 and Pratt-Johnson, 29 the suppressed region was not limited to the central part of the binocular field, but was relatively diffuse, extending throughout the central 208.…”

A Limited Role for Suppression in the Central Field of Individuals with Strabismic Amblyopia

“…The impact of measurement method on the result was elegantly demonstrated by Mehdorn [23] who could find no evidence for suppression in eight individuals using stereoperimetry, a technique which establishes if stereopsis can be revealed when disparate images are presented separately to the two eyes. The idea is that the perception of depth can only arise if the right and left eye percepts are combined; hence the depth percept cannot arise if suppression exists at that visual field location and presenting targets either in front or behind the reference plane provides a psychophysical means of testing that depth is in fact being seen.…”

A Pilot Study Examining Density of Suppression Measurement in Strabismus

“…1 However, the size and depth of this suppression scotoma can vary between individuals with type of strabismus 1-4 and measurement method. [3][4][5][6][7][8] Less dissociative measurement techniques or more similar retinal images are thought to give rise to larger and/or denser suppression scotomata, 2,7 however, this is not a universal finding. 5 Amblyopia density can also have an impact, 9 although again this was not found in all studies.…”

“…In the research arena, density of suppression has been measured using stereoscopic microperimetry, 3,4 orthogonal gratings, 9 and phased image changes. 7 However, the techniques used above rely on the existence of some form of binocular vision, however abnormal, or rapid alternating suppression, 9 and have primarily used individuals with microtropia for study, although techniques such as static binocular perimetry 2,5,11 and dichoptic contrast balancing [12][13][14] can be used in individuals with a larger angle strabismus and no fusion.…”