Merck Manual

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Some Causes and Features of Unequal Pupils

Some Causes and Features of Unequal Pupils


Common Features*

Adie (tonic) pupil (a pupil that does not constrict normally in response to light)

One or both pupils are too wide, do not fully constrict in response to light, and widen slowly after being constricted by light

No other symptoms

Argyll Robertson pupil

Pupil that constricts better to accommodation (when a doctor's finger moves towards the eye) than to light

History of syphilis

Birth defects of the iris

Features that are present lifelong

Usually other birth defects

Chemicals and drugs (including scopolamine patches, cocaine, pilocarpine, drugs in animal flea collars or sprays, certain aerosol drugs for asthma or COPD such as ipratropium or tiotropium, and organophosphate insecticides) if they contact the eye and some eye drops

In people who use or have been exposed to these substances

Sometimes difficulty focusing, particularly on nearby objects

On one side of the face, a drooping eyelid, a small pupil that is slow to widen in response to darkness, and decreased sweating

If the cause of Horner syndrome is a disorder (such as migraines or a lung tumor) or an injury, other symptoms

An eye injury or eye surgery

In people who have had an eye injury or eye surgery

Sometimes pain with exposure to bright light and/or eye redness

Physiologic anisocoria (pupils that are normally different sizes)

Present for a long time

No symptoms or abnormalities found during the examination

A difference of less than 1/16 inch (about 1 millimeter) in pupil size and pupils that constrict normally in response to light

Double vision and a drooping eyelid

Sometimes, in people who have had a head injury or who have a bulge (aneurysm) in an artery supplying the brain, bleeding in the brain, diabetes or hypertension that affects the blood vessels, or a brain tumor

* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present.

COPD = chronic obstructive pulmonary disease.