What is a Tonic Pupil?
Tonic pupil is a pupil abnormality in which the pupil is dilated and does not respond to light appropriately. In a tonic pupil, the affected pupil appears larger and it does not constrict when light is shined in the eyes. Tonic pupil is due to the improper functioning of the ciliary ganglion behind the eye. A tonic pupil can be caused by conditions including Adie’s tonic pupil, oculomotor nerve palsy, and pharmacological dilation.
- Tonic pupil refers to an abnormal pupil that appears dilated (large) and has poor constriction (narrowing) in response to bright light.
- Tonic pupil is due to dysfunction of the ciliary ganglion, fibers that control the parasympathetic pathway of pupil constriction and accommodation (focusing).
- Adie’s tonic pupil is diagnosed in an eye exam by measuring pupil sizes, observing pupil response to light, and instilling pilocarpine eye drops.
Understanding the Tonic Pupil
A tonic pupil is caused by injury or damage to the ciliary ganglion. The ciliary ganglion controls parasympathetic innervation to the eye, which includes constriction or shrinking of the pupil in response to light (miosis) and constriction of the pupil in response to looking at a near object (accommodation). Nerve fibers travel through the oculomotor nerve (Cranial Nerve III), synapse at the ciliary ganglion, and then go on to innervate the iris sphincter and ciliary body. If there is Adie’s tonic pupil, the ciliary ganglion is damaged and the affected eye is unable to constrict or focus with the same speed and strength as the other eye.
Symptoms of Tonic Pupil
Normal eye pupil behavior allows pupils to enlarge (dilate) in low-light conditions and shrink (constrict) in high-light conditions. The primary symptom of Adie’s tonic pupil is a pupil that appears larger than the other pupil and does not respond to light by getting smaller.
Additional Adie’s tonic pupil symptoms can include:
- Anisocoria: different pupil sizes of both eyes
- Blurry vision when reading, and trouble focusing on near objects
- Light sensitivity
Other visual and neurological disorders can also cause these symptoms. If you observe a pupil’s size change or experience any unanticipated problems with your vision, it’s crucial to visit your eye doctor.
Most tonic pupil cases are idiopathic, which means they have no recognized cause.
Other causes include:
- Adie’s tonic pupil
- Tumor of the ciliary ganglion
- An oculomotor nerve palsy
- Pharmacological dilation from medications such as Visine, Benadryl, or cocaine
- Pharmacological dilation from plants such as angel’s trumpet
- Autoimmune conditions
- Viral or bacterial infection
- Problems following eye surgery
- Eye injury
How is a Tonic Pupil Identified?
Adie’s tonic pupil is diagnosed by an eye doctor. Commonly, an ocular pharmaceutical agent called pilocarpine is used to diagnose a tonic pupil. Pilocarpine is an eye drop that is instilled into the affected dilated eye. For the purpose of diagnosing a tonic pupil, a very diluted form of 0.125% pilocarpine is used. This low concentration of pilocarpine does not cause any response in a normal eye. However, if Adie’s tonic pupil is present, the diluted pilocarpine will cause miosis, or constriction of the pupil.
The ophthalmologist may also:
- Shine light into the eyes to ascertain if the pupils constrict to light appropriately.
- Measure the pupil size in both light and dark conditions.
- Measure the accommodative response by asking the patient to focus on a near object placed close to the eyes.
- Observing the iris for “worm-like” movement using a magnifying slit lamp microscope.
- Testing the extraocular eye muscle coordination.
Treatment options for Adie’s tonic pupil are limited. The majority of treatment focuses on symptom control. For example, your ophthalmologist might advise:
- Sunglasses or tinted contact lenses for light sensitivity
- Eye drops to lessen light sensitivity and glare
- Possible referral to a neuro-ophthalmologist for further testing