Pupillary Disorders

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Pathway of pupillary dilatation (sympathetic)

Hypothalamus

Hypothalamus

Ciliary ganglion

Internal carotid artery

\ Superior cervical ganglion

Cervical sympathetic chain

Ciliary ganglion

Internal carotid artery

\ Superior cervical ganglion

Cervical sympathetic chain

Sympathetic fibres descend from the ipsilateral hypothalamus through the lateral aspect of the brain stem into the spinal cord. The pupillary fibres pass out in the anterior roots of C8 and Tl, enter the sympathetic chain and, in the superior cervical ganglion, give rise to postganglionic fibres which ascend on the wall of the internal carotid artery to enter the cranium. The fibres eventually leave the intracranial portion of the internal carotid artery and pass directly through the ciliary ganglion to the iris or join the cranial nerves III, IV, V and VI, running to the eye and iris. Sudomotor fibres (concerned with sweating) run up the external carotid artery to the dermis of the face.

Interruption of sympathetic supply affects:

1. Pupillary dilatation causes a small pupil (miosis)

2. Levator palpebrae muscle (30% supplied by sympathetic) causes drooping of eyelid (ptosis)

3. Vasoconstrictor fibres to orbit, eyelid and face causes absence of sweating. Interruption of parasympathetic supply affects'.

Pupil constriction causing a large pupil (mydriasis)

Mechanism of accommodation

When gaze is focused on a near object the medial rectus muscles contract, producing convergence, the ciliary muscles contract enabling the lens to produce a more convex shape and the pupil constricts (accommodation for near vision).

The pathway is poorly understood but must /

involve the visual cortex, Edinger-Wcstphal nuclei Vv^J^5 ■ ^

and both medial rectus components of the III \ /

nerve nucleus in the midbrain. ^ ^

Inability of the pupil to constrict during accommodation need not always be associated with impairment of convergence, though usually this is the case.

Pupillary Inequality (Anisocoria)

A difference in pupil size occurs in 20% of the normal population and is distinguished from pathological states by a normal response to bright light.

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