The lower eyelid may rest at a higher level than normal, called inverse ptosis. In combination with the drooping of the upper eyelid, this reduces the opening between the upper and lower eyelids. When a person is in darkened surroundings, the normal pupil will automatically enlarge, or dilate quickly to improve vision. For a person with Horner's syndrome, the affected pupil will take longer to dilate in these conditions, making the difference in pupil size more obvious in the dark. This is called dilation lag. Horner's syndrome may also cause redness of the affected eye, problems with vision, including double vision, and lower the pressure within the eye. In children with Horner's syndrome, the iris on the affected side may be a different color than the normal side due to lack of pigment. Other symptoms not related to the eye depend on the underlying condition. These may include difficulty walking, weakness or numbness on one side of the body, pain in the arm or hand, hoarseness, and difficulty swallowing.
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