Alignment ability of strabismic and eye enucleated subjects on the horizontal and oblique meridians

For normal sighted observers visual performance is often superior on the principal meridians than on the oblique. There has been no clear consensus on whether disruption of the visual system affects performance on orientation sensitivity tasks. Here we compare the abilities of normally sighted subjects tested monocularly, subjects with one eye enucleated and strabismic subjects using the non-deviating eye, in an orientation task. Subjects were asked to align a dot with a bar that was oriented either horizontally or on the oblique. For all groups, alignments were significantly more accurate and precise for the horizontal bar as compared to the oblique bar. Normally sighted subjects were significantly more precise on alignments in the horizontal and oblique planes than strabismic subjects, using the non-deviating eye. Precision for eye enucleated subjects was similar to that of normally sighted subjects. Precision of alignments did not correlate to the age at diagnosis of strabismus or to depth of amblyopia in strabismus. We conclude that for alignment ability, the disruption of visual development produced by enucleation of one eye is not equivalent to that produced by strabismus. This could represent an underlying difference in the visual system between these two groups.