Tonic pupil

Tonic pupil, also known as Adie's pupil, is a neurological condition characterized by a pupil that reacts slowly to light but has a more normal and quicker response to accommodation, i.e., focusing on an object. This condition is typically unilateral, affecting one eye, but can occasionally be bilateral.

Etiology

The exact cause of tonic pupil is unknown. However, it is believed to be due to damage to the postganglionic fibers of the parasympathetic nervous system that innervate the iris sphincter muscle. This damage can be caused by an autoimmune or viral infection.

Symptoms

The primary symptom of a tonic pupil is anisocoria, a condition characterized by unequal pupil sizes. The affected pupil will be larger than the other, especially in bright light. Other symptoms may include blurred vision, difficulty focusing on close objects, and light sensitivity.

Diagnosis

Diagnosis of tonic pupil is primarily clinical, based on the characteristic signs and symptoms. The Holmes-Adie syndrome is diagnosed when tonic pupil is accompanied by absent or diminished deep tendon reflexes. A pharmacological test using a dilute solution of pilocarpine, a medication that constricts the pupil, can also be used to confirm the diagnosis.

Treatment

There is no specific treatment for tonic pupil. Management is primarily symptomatic, focusing on alleviating any discomfort caused by light sensitivity with sunglasses or pupil-constricting eye drops. In some cases, the condition may improve on its own over time.

Prognosis

The prognosis for individuals with tonic pupil is generally good. While the condition is typically chronic, it does not lead to blindness or any serious complications. However, it can cause some functional impairment, particularly in bright light conditions.

See also

• Anisocoria
• Holmes-Adie syndrome
• Pilocarpine