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Sir,

We report an unusual case of episodic mydriasis with segmental pupillary distortion.

Case report

A 33-year-old lady presented complaining of an intermittently irregular right pupil. The pupil distortion usually lasted for a few minutes and, despite being painless, was often accompanied by a vague change in periocular sensation. The symptom occurred sporadically, sometimes with several weeks in between episodes, but occasionally happening several times on the same day. There were no other visual symptoms and no significant past ocular history. General health was good and no regular medications were taken.

On examination, visual acuity was normal bilaterally. There was a 1 mm right ptosis with mild anisocoria, the right pupil being 1 mm smaller in normal room illumination. In dim lighting, the discrepancy in pupillary size increased to 3 mm. Pupil reactions to light and accommodation were considered normal. No other ocular or neurological abnormalities were detected.

Gutt. Phenylephrine 10% in both eyes appeared to improve the ptosis and caused more dilatation to the right pupil (7 mm compared to 4 mm on the left). A provisional diagnosis of a variant of right Horner's syndrome was made. A chest X-ray and magnetic resonance imaging of the brain and orbits were both normal. Some weeks later, the patient captured a picture of the pupillary distortion (Figure 1) confirming the diagnosis of a tadpole-shaped pupil.

Figure 1
figure 1

Tadpole-shaped pupil.

Full size image

Comment

Thompson et al1 gathered and reported on 26 cases of intermittent pupillary abnormality, one segment of iris being temporarily pulled to a peak before returning to normal. The patients were predominantly women, aged 28–48 years. Most cases were accompanied by a degree of visual blurring along with unusual sensations such as an ache, a ‘ping’ in the eye, or chill on the face.

The brief pupil irregularity was seldom witnessed by a physician. However, on the rare occasions when an episode occurred during an examination, a peaked segment that reacted poorly to light was observed, the rest of the pupil constricted normally. Assessing pupillary behaviour in between episodes, a large number of patients had signs consistent with Horner's syndrome and to a lesser extent Adie's pupil.

The authors named the condition tadpole-shaped pupil and felt that the appearance resulted from a focal spasm of the iris dilator muscle. The aetiology remains unclear, although it is postulated that the cause is of benign neural origin.