An Interesting Case of Pupillary Changes During the Testing of Ocular Movements and its Influence on the Diagnosis?

To describe an unusual case presentation of a decompensating exotropia with an incidental pupil anomaly highlighting the importance of observing pupils during the assessment of ocular movements. A case whose signs included an exotropia and an enlarged tonic pupil which were initially mistaken for an atypical case of Oculomotor nerve palsy, triggering immediate imaging investigations. We discuss how understandable it would be for experienced clinicians to arrive at this case's misdiagnosis and how it could have been avoided thereby helping to preserve where possible costly resources of neuro imaging and inpatient stays.

A 71 year old man who was seen as a tertiary referral case by the Queen Elizabeth Hospital Birmingham's (QEHB's) neuro-ophthalmology service, where a second opinion for the patient was sought from a neurology team from another hospital. He was seen by the orthoptist and neuro-ophthalmologist consultant.

On presentation at QEHB visual acuity measured 6/9 Snellens in each eye with varifocals, improving to 6/6 with pinhole testing, the fundi and optic discs were normal. Anisocoria was noted with the left pupil being larger than the right pupil. Orthoptic assessment revealed a small angle left exotropia on cover test, increasing in size on alternate cover test with a blink type recovery to its original angle. An orthoptic diagnosis of a decompensating left microexotropia with identity was given. In the left eye there was a slight mechanical restriction in adduction, underacting superior rectus and a larger underacting inferior rectus with an "A" type alphabet pattern with symptoms of horizontal diplopia on all right gaze positions. There was no evidence of ptosis, convergence was intact and saccades were fast and appeared of a normal velocity. The anisocoria appeared more obvious when the patient looked to right gaze where his left pupil seemed to enlarge further. Assessment of the pupillary function led to the patient being diagnosed as having bilateral asymmetrical Adies (tonic) pupils.

This case highlights the importance of not only carrying out a detailed pupil reaction assessment but also the necessity of observing the pupils during the assessment of ocular movements. This case highlights how anisocoria can mislead a clinician's attention to believing that only one particular pupil is abnormal where as it could be both. Also it highlights that the classic combination of symptoms and observations of diplopia, exotropia, longstanding incomitance and anisocoria in terms of a dilated pupil may not necessarily be an Oculomotor cranial nerve palsy and requiring the patient to undergo imaging investigations on an urgent basis may be avoided.