Symptoms

Horner syndrome usually affects only one side of the face. Common signs and symptoms include:

• A persistently small pupil (miosis)
• A notable difference in pupil size between the two eyes (anisocoria)
• Little or delayed opening (dilation) of the affected pupil in dim light
• Drooping of the upper eyelid (ptosis)
• Slight elevation of the lower lid, sometimes called upside-down ptosis
• Sunken appearance to the eye
• Little or no sweating (anhidrosis) either on the entire side of the face or an isolated patch of skin on the affected side

Signs and symptoms, particularly ptosis and anhidrosis, may be subtle and difficult to detect.

Children

Additional signs and symptoms in children with Horner syndrome may include:

• Lighter iris color in the affected eye of a child under the age of 1
• Lack of redness (flushing) on the affected side of the face that would normally appear from heat, physical exertion or emotional reactions

When to see a doctor

A number of factors, some more serious than others, can cause Horner syndrome. It is important to get a prompt and accurate diagnosis.

Get emergency care if signs or symptoms associated with Horner syndrome appear suddenly, appear after a traumatic injury, or are accompanied by other signs or symptoms, such as:

• Impaired vision
• Dizziness
• Muscle weakness or lack of muscle control
• Severe, sudden headache or neck pain