Tonic pupil secondary to varicella-zoster-virus (VZV) keratouveitis in a child

Abstract

Abstract Introduction: An unusual case of tonic pupil in a 4-year-old male child secondary to Varicella-Zoster-Virus (VZV) keratouveitis is described in this case report. To the best of our knowledge, our report is the thirtieth case of tonic pupil following chickenpox infection in the literature. Patient concerns: A 4-year-old male child presented at our department in June 2019 with anisocoria and feeling generally unwell. The right pupil was noted by his mother to be larger than the left in normal, bright and dim illumination conditions. Of note, the child at the same time was suffering from chickenpox and the symptoms started approximately 4 days prior to the attendance at Accident and Emergency with a generalized vesicular rash. The mother also reported that the right eye was mildly red and uncomfortable and her son was complaining of photophobia. Diagnosis: Tonic pupil secondary to VZV keratouveitis. Interventions: Full past medical and ocular history was obtained. The patient underwent full ophthalmic examination including dilated fundoscopy. Visual acuity was recorded with Snellen Chart and Keeler chart of Minimum Angle of Resolution chart. Patient had Magnetic Resonance Imaging due to anisocoria to exclude intracranial pathology. The child was treated with intravenous Acyclovir and had a good recovery, though the anisocoria persisted. Outcomes: During the follow-ups in the Paediatric Ophthalmology Clinic, 0.125% pilocarpine test revealed profound miosis of the affected right pupil and normal response from the healthy left pupil. In addition, the range of accommodation was reduced in the affected right eye. The child was closely observed to prevent right eye amblyopia and the plan was to issue bifocals to maximize both near and distant visual acuity. Nevertheless, during close follow-up the accommodation reflex in the right eye recovered on its own and the child was eventually discharged from the clinic without executive bifocals. Conclusion: VZV keratouveitis leading to tonic pupil is a rare complication. The proposed pathophysiological mechanism is retrograde dissemination of the infection through the parasympathetic nerve fibers from the iris via the inferior branch of the third nerve to the ciliary ganglion. Our case emphasizes the potential amblyogenic consequences of tonic pupil.