Review of Cornea

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Elongated Pupil Looks Fishy

A patient reports episodes of an unusual, vertically elongated pupil. Is it for real? If so, is it serious?
Edited by Paul C. Ajamian, O.D.


A patient presented with a complaint that her pupil looks like a cats eye for several minutes and then returns to normal. She says this happens several times a day. Is this patient imagining this, or is she truly experiencing a clinical condition?

A: Several clinical conditions can cause intermittent anisocoria, says optometrist Joseph M. Rappon, of Conyers, Ga. These include Adies and Horners syndromes, benign episodic unilateral mydriasis, pharmacologic misadventure and something known as tadpole-shaped pupil.

Among these conditions, accidental exposure to a cholinergic agonist is the most commonly encountered, Dr. Rappon says. So, a thorough case history is essential to rule this out.

The next condition to rule out is benign episodic unilateral mydriasis (BEUM), he says. This uncommon condition arises from what is probably a heterogeneous group of conditions that result in either para-sympathetic deficiency or sympathetic hyperactivity.1 More commonly found in females, BEUM is very often associated with blurred vision, headache or orbital pain, and may be a limited form of an ophthalmoplegic migraine.2 The median duration of this condition is 12 hours with a frequency of two to three episodes per month.1

However, neither BEUM, Adies nor Horners syndromes cause an irregular pupil shape, Dr. Rappon says. The next most likely condition is tadpole-shaped pupil. This uncommon condition is typically unilateral and mainly affects females. It causes a distortion of the pupil that usually lasts less than two minutes and occurs several times per day, sometimes for weeks at a time.3

Although tadpole-shaped pupil resolves spontaneously, Dr. Rappon says, these clusters of pupil distortion may recur weeks or months later. Patients experience an unusual sensation in or around the affected eye during the episode, and some report blurred vision during each event.3 
The patients left eye with tadpole pupil.

Q: Should I comanage this patient with a neurologist or neuro-ophthalmologist?

A: The irregular pupil is caused by a focal spasm of the iris dilator muscle, probably due to neural stimulation rather than from a muscular origin, Dr. Rappon says. Although this is a benign event that does not require further medical evaluation, you should perform a complete ocular examination including pupillary testing and a full-threshold visual field exam, he says.

The associated conditions of tadpole-shaped pupil are Adies syndrome, Horners syndrome and migraine, Dr. Rappon says. All are seen in a high percentage of patients who have tadpole-shaped pupil, though it is not known how or to what extent these conditions affect pupillary distortion. Also, application of 10% phenylephrine can clinically replicate tadpole-shaped pupil, he says.3 Again, be sure to rule out pharmacological exposure.

If you suspect one of these associated conditions but are unable to confirm them yourself, make a neurological referral, Dr. Rappon says. Enumerate your findings to the neurologist or neuro-ophthalmologist, as well as what tests you would like performed and/or which conditions you wish to be ruled out, he says. Patient reassurance is the only current management.

Remember, Dr. Rappon says, patients say a lot of crazy things. But as unlikely as their symptoms sometimes seem, some are indeed real. So all patients need to be treated with respect and their complaints taken seriously, he says.

1. Jacobson DM. Benign episodic unilateral mydriasis. Clinical characteristics. Ophthalmology 1995 Nov;102(11): 1623-7.
2. Balaguer-Santamaria JA, Escofet-Soteras C, Chumbe-Soto G, Escribano-Subias J. Episodic benign unilateral mydriasis. Clinical case in a girl. Rev Neurol 2000 Oct;31(8):743-5.
3. Thompson HS, Zackon DH, Czarnecki JS. Tadpole-shaped pupils caused by segmental spasm of the iris dilator muscle. Am J Ophthalmol 1983 Oct;96(4):467-77.

Vol. No: 142:10Issue: 10/15/2005

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