TONIC PUPIL

SIGNS AND SYMPTOMS
The patient often complains of unequal pupil sizes, and frequently of decreased vision at near. The patient may be any age, especially if there has been history of local trauma or orbital surgery. Often when a history of trauma is not apparent, the patient will be younger and female.

A tonic pupil may occur in one or both eyes. It is typically larger than the normal fellow pupil in normal illumination. However, there is no significant change in size of the tonic pupil when going from bright to dim illumination. The tonic pupil will appear fixed and unreactive to light.

When testing near accommodation, the tonic pupil will show a slow constrictive response. Biomicroscopy often reveals segmental paralysis and flattening of the pupil border, which gives the pupil an irregular shape. There may also be a vermiform movement of the non-paralyzed sections of the iris. In cases of idiopathic tonic pupils, deep tendon reflexes often diminish, particularly in young females.

PATHOPHYSIOLOGY
A tonic pupil results from damage to the ciliary ganglion within the orbit. In the ciliary ganglion, 93 percent of the post-ganglionic fibers innervate the ciliary body for accommodation; the remaining 7 percent innervate the iris sphincter for miosis during the light reflex. When the ciliary ganglion is damaged, there is an aberrant regeneration of fibers, with post-ganglionic fibers that originally innervated the iris sphincter now innervating the ciliary body. Thus, light response is diminished, but accommodative near constriction remains. However, near constriction is often slow and segmental, and accommodation is often diminished.

Trauma is the most common cause of a tonic pupil. Other causes associated with tonic pupils include viral illness, diabetes, syphilis and giant cell arteritis. When the etiology cannot be identified, particularly in young females, the condition is termed Adie's tonic pupil.

MANAGEMENT
There is no exact management plan for tonic pupils. Address each case individually. If the patient dislikes the cosmetic asymmetry of the pupils, consider opaque contact lenses. For a patient over 60 who develops a tonic pupil, order an erythrocyte sedimentation rate (ESR) to check for giant cell arteritis. If the patient is male, and has bilateral tonic pupils, order both a specific (FTA-ABS) and non-specific treponemal (RPR) test to examine for syphilis. In most cases, try to elicit a history of trauma.

CLINICAL PEARLS

Remember that a tonic pupil in an elderly patient can be caused by giant cell arteritis, and order an ESR. This can help diagnose a vision-threatening disease before severe vision loss ensues from ischemic optic neuropathy.

Incidence of syphilis is about 45 percent in cases of bilateral tonic pupils in males. Order both a specific and non-specific treponemal test for diagnosis.

In cases of Adie's tonic pupils, testing of patellar tendon reflexes can assist in the diagnosis.

Not all tonic pupils are Adie's tonic pupils. This term is mistakenly overused. The term "Adie's tonic pupil" refers to an idiopathic tonic pupil.