Anisocoria is unequal pupil size. The pupil is the black part in the center of the eye through which light passes.

Occasionally, a baby is born with different sized pupils and there is no underlying disorder. If other family members also have this condition, then pupil size is possibly genetic and is nothing to worry about.

At times, for unknown reasons, pupils may differ in size. If there are no other symptoms and if the pupils return to normal, then the temporary condition is nothing to worry about.

Unequal pupil sizes that develop later in life and persist are often a sign of a brain, blood vessel, or nerve disease.

The use of eyedrops are a common cause of a harmless change in pupil size. Other medicines that get in the eyes, including medicine from asthma inhalers, can change pupil size.

Other causes of unequal pupil sizes may include:

• Bleeding inside the skull caused by head injury
• Brain tumor or abscess
• Infection of membranes around the brain caused by meningitis or encephalitis
• Aneurysm
• Excess pressure in one eye caused by glaucoma
• Tumor in the chest or lymph node pressure that may be accompanied by decreased sweating, a small pupil, or drooping eyelid all on the affected side

Treatment depends on the cause unequal pupil size. You should see a doctor if you have sudden changes in pupil size. The new development of different sized pupils may be a sign of a very serious condition.