Purpose/methods: Tonic pupils in early childhood are rare. We studied an otherwise healthy 31/2-month-old girl who had a right pupil that was poorly reactive to light, without other signs of oculomotor nerve palsy.
Results/conclusions: Constriction of the right pupil after instillation of 0.125% pilocarpine eyedrops confirmed denervation hypersensitivity, consistent with a tonic pupil. There was no strabismus or proptosis. A magnetic resonance imaging scan demonstrated a right orbital mass, interposed between the lateral and inferior recti muscles. Biopsy was consistent with a benign, glial-neural hamartoma. Thus, in this young patient, a tonic pupil was associated with a benign orbital mass.