The pupil in congenital third nerve misdirection syndrome.

The involved pupil in the syndrome of aberrant regeneration of the oculomotor nerve usually remains larger than the uninvolved side, or approaches equality in size. A 4-year-old child was seen with congenital aberrant regeneration of the right third nerve. The right pupil was consistently smaller than the left, but particularly so in dim illumination. The question can be raised as to whether relative pupillary miosis more commonly follows third nerve misdirection in children than adults.