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 of the affected eye
Little or no sweating (anhidrosis) on the affected side of the face
 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
Change in color on the affected side of the face that would typically appear from heat, physical exertion or emotional reactions
