[Attention shifting and dissociated vertical squint].

Some patients with dissociated vertical deviation show an increasing upward drift of their squinting eye when reading small numbers at a distance of 5 m, making a special effort to shift attention to the non-squinting eye. This finding is at variance with the view that the manifestation of dissociated vertical deviation may be induced by visual inattention. The phenomenon could be explained by analogy to the occlusion test, by a binocular imbalance in visual information processing. The phenomenon may be found frequently in patients who require surgery for an especially disfiguring intermittent vertical squint. Looking for the phenomenon may be useful when deciding whether to operate for a dissociated vertical deviation: If increasing vertical deviation is observed during binocular acuity testing, surgical treatment should be considered.