Tadpole Pupil

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Article initiated by:

Salar Rafieetary, M.D., Shane Marsili, Lauren Ditta M.D.

All contributors:

Nagham Al-Zubidi, MD, Salar Rafieetary, M.D., Danah Albreiki, MBBS FRCSC

Assigned editor:

Danah Albreiki, MBBS FRCSC

Review:

Assigned status Up to Date

 by Danah Albreiki, MBBS FRCSC on December 9, 2024.

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Contributing Editors:	add

Disease Entity

Tadpole Pupil, Tadpole-Shaped pupil

Disease

Tadpole pupil (also referred to as tadpole-shaped pupil) is a rare condition that refers to episodic pupillary distortion resulting in a tadpole shaped pupil. This was originally described by Thompson et al. in a series of patients. The hallmark feature is that one segment of the iris is pulled to a peak, creating an irregular shaped pupil, resembling the shape of a tadpole. At present, only 45 cases have been reported in the literature.

Pathophysiology

The pathophysiologic mechanism of tadpole pupil is unknown. A few hypotheses have been reported, but none have been proven. The association of tadpole pupil and Horner Syndrome allows for speculation that denervation hypersensitivity plays a role. While several cases of tadpole pupil have been reported without an identifiable trigger, physical exercise and waking up from sleep have been reported, leading to the hypothesis that an increase of circulating catecholamines may play a role.

Risk Factors

There are no known risk factors for tadpole pupil. Episodes of tadpole pupil have been associated with migraine headache, menstruation , awakening from sleep, exercise, strabismus surgery, and hyponatremia with seizures. The most common association with a tadpole pupil is a Horner syndrome, however Adie's has also been reported as an association.

Diagnosis

Tadpole pupil is a clinical diagnosis based on history and the hallmark of episodic pupillary sphincter dilation. As mentioned above, the episodes are typically brief and are more often unilateral, but can be bilateral and can rarely occur simultaneously.

Dilute pilocarpine testing can be used in the office to rule out Adie’s pupil. An exaggerated constriction post-pilocarpine would make the diagnosis of Adie’s, not tadpole pupil. On the contrary, the absence of the phenomenon along with the features listed above would support a diagnosis of tadpole pupil.

Approximately 42% of the patients in Thompson’s series had a concurrent Horner’s syndrome. Apraclonidine testing can be performed to detect Horner’s syndrome. A normal pupil will constrict in response to Apraclonidine due to the alpha 2 agonistic properties. However, when Horner’s syndrome is present, the pupil will dilate due to the alpha 1 agonistic properties, leading to reversal the anisocoria. It is also important to obtain a thorough medical history and review of symptoms in order to detect any central, second order neuron or third order neuron lesion. When appropriate, imaging of the brain and/or thorax should be obtained.

The pupil will appear oval shaped and tapered at the end most near the limbus. The tapered end can appear in any clock direction of the eye.

History

The duration of the episode is around five minutes or less (79%). It occurs spontaneously in 91% of the cases, and is associated with blurry vision or a peculiar sensation of the eye or face on the ipsilateral side in 72% of the cases. In the non spontaneous cases, precipitating factors included strabismus surgery, morning awakening, physical exercise, and hyponatremia with seizures. The episodes may occur in 10-50 times a day, and may also occur in clusters. Most cases resolved spontaneously, while some patients had occasional relapses. unilaterality was present in most cases (93%), and bilaterally was rare. Alternating cases were seen in 23% of patients.

Physical examination

Episodes of tadpole pupil are rarely witnessed by the physician. With the modern use of cameras and camera phones, more of these episodes are being documented and reported to ophthalmologists with photographs or videos.

The clinician must pay careful attention to visual acuity, pupils (both in dark and light), assessing for uniform constriction and dilation and assessing for any vermiform movements of the iris. When episodes of tadpole pupil were observed by the clinician, there was poor constriction to light at the segment of dilated iris, but the remainder of the pupil constricted normally, suggesting abnormal activity of the iris dilator as opposed to iris sphincter.

Iris color should be evaluated assessing for any signs of heterochromia (i.e. Congenital Horner’s), iris atrophy (i.e. trauma), or transillumination defects. Eyelid symmetry and extraocular movements should be assessed. Needless to say, a full neuro-ophthalmic exam should be performed.

Differential diagnosis

The differential diagnosis for tadpole pupil includes:

• Benign episodic unilateral mydriasis
• Horner’s syndrome
• Adie pupil
• Argyll Robertson Pupil
• Unilateral exposure to mydriatic agent
• Ocular migraine
• Coloboma
• Iris sphincter damage (post-traumatic or post-surgical)
• Anterior uveitis
• Open globe

Management and Complications

Because of the paucity of reported cases, no randomized studies have been performed on potential treatment options. Most reported cases resolved spontaneously. Tadpole pupil requires no medical or surgical management. There are no known complications. If an associated Horner syndrome has been ruled out, patients can be reassured that episodes of tadpole pupil while bothersome to some patients will not have any long term adverse effects on vision.

Prognosis

Long term follow-up with these patients has not been reported in the literature. Patients usually have long term resolution with occasional relapses. It has yet to be reported at what time interval patient’s begin to experience resolution of symptoms.

References

7. Koay KL, Plant G, Wearne MJ. Tadpole pupil. Eye. 2004;18(1):93-94. doi:10.1038/sj.eye.6700513