Horner’s Syndrome.

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The sympathetic nerves to the eye are

occasionally interrupted. Interruption frequently occurs

in the cervical sympathetic chain. This causes the clinical

condition called Horner’s syndrome, which consists

of the following effects: First, because of interruption of

sympathetic nerve fibers to the pupillary dilator muscle,

the pupil remains persistently constricted to a smaller

diameter than the pupil of the opposite eye. Second, the

superior eyelid droops because it is normally maintained

in an open position during waking hours partly

by contraction of smooth muscle fibers embedded in the

superior eyelid and innervated by the sympathetics.

Therefore, destruction of the sympathetic nerves makes

it impossible to open the superior eyelid as widely as

normally.Third, the blood vessels on the corresponding

side of the face and head become persistently dilated.

Fourth, sweating (which requires sympathetic nerve

signals) cannot occur on the side of the face and head

affected by Horner’s syndrome