Contrast Letter Thresholds in the Non-affected Eye of Strabismic and Unilateral Eye Enucleated Subjects

To investigate the effects of visual disruption on contrast letter thresholds of the non-affected eye, subjects with one eye enucleated, strabismic subjects using the non-deviating eye and normal control subjects were asked to identify letters on eye charts and single letter cards which varied in contrast (between 4 and 96%) and size. At all contrast, contrast letter acuity of eye enucleated subjects was superior to both normal control subjects and strabismic subjects. Early onset strabismic subjects (onset < 24 months) showed inferior performance to normal control subjects at all contrasts of 25% and above. Late onset strabismic subjects showed normal performance at all contrasts, except for high contrast single letters, where performance was inferior to normal control subjects. Further, for all subjects groups, performance on letter charts was similar to performance on single letter cards. We conclude that disruption to the visual system caused by eye enucleation or strabismus is not equivalent. These differences may be due to intrinsic differences between the visual systems of eye enucleated subjects and strabismic subjects and/or to the profound differences in deprivation caused by the two conditions.