The Near Response Convergence Pupilloconstriction Accommodation

When a subject watches an approaching object, three things happen: the eyes converge through the action of the medial rectus muscles; the pupils constrict; and the curvature of the lens increases through the action of the ciliary muscle (accommodation). The near response may be initiated voluntarily (by squinting) but is most often the result of a reflex, whose afferent arm consists of the visual pathway to the visual cortex. The efferent arm for convergence consists of descending fibers to the pretectal convergence center (Perlia's nucleus) and onward to the oculomotor nucleus (nuclear area for the medial rectus muscles); the efferent arm for pupilloconstriction and accommodation is the parasympathetic projection of the Edinger-Westphal nucleus through the oculomotor nerve to the sphincter pupillae and ciliary muscles.

Dilator muscle

Lens-

Sphincter — muscle

Zonular fibers

Ciliary muscle (short ciliary ner-

ves)l

Pupil

Ciliary ganglion

Levator palpebrae

Parasympathetic fibers -Pial vessels

-Oculomotor n.

Visual cortex (areas 17, 18, 19)

Dilator muscle

Lens-

Sphincter — muscle

Pupil

Ciliary ganglion

Levator palpebrae palpebrae superioris m. (III) / / superioris m. (III)

Medial rectus muscle

Superior tarsal m.

Orbicularis oculi m. (VII)

Pleural dome

Levator Palpebrae

Subclavian a.

palpebrae superioris m. (III) / / superioris m. (III)

Medial rectus muscle

Superior tarsal m.

Dilator muscle

Conjunctival vessels

Orbicularis oculi m. (VII)

Pleural dome

Parasympathetic fibers -Pial vessels

-Oculomotor n.

Vasa nervorum

Visual cortex (areas 17, 18, 19)

Perlia's nucleus

Pretectal area

Lateral geniculate body

Light reflex Accommodation Convergence

-Edinger-

Westphal nuclei

Sweat glands (forehead)

Orbitalis m.

Central sympathetic pathway

Carotid plexus, internal carotid a.

Superior cervical ganglion

Sudoriparous and vasomotor fibers to skin of face traveling along the external carotid a.

Middle cervical ganglion

Inferior cervical (stellate) ganglion

Ciliospinal center Ansa subclavia

Subclavian a.

Pupillomotor Function

Examination. The size and shape of the pupils are first assessed in diffuse light with the patient looking at a distant object to prevent the near response. The room is then darkened and the direct light reflex of each pupil is tested at varying light intensities (by varying the distance of the lamp from the eye). If both pupils constrict when illuminated, there is no efferent pupillary defect. Next, in the swinging flashlight test, the examiner indirectly illuminates one eye with a bright light for ca. 2 seconds, then quickly switches the light to the other eye, and back again, some 5-7 times. The normal finding is that the two pupils are always of equal diameter; an abnormal finding indicates asymmetry of the afferent arm of the light reflex on the two ¡3 sides, e.g., because of an optic nerve lesion C (Marcus Gunn pupillary escape phenomenon). If either of these tests is abnormal, or if the pupils "g are significantly unequal, the near response 'c should be tested and the direct and consensual 2 light reflexes should be tested separately in each eye. It is easier to identify which pupil is abnormal by observing both phases of the light response (constriction and dilatation): both are slower in the abnormal pupil. In light-near dissociation, the pupils constrict as part of the near response, but not in response to light. Pharmacological pupil testing may be necessary in some cases.

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