Accommodation

Accommodation (Fig. 36) involves a neural circuit to the visual cortex and back, which makes sense, for we need our cerebral cortex to determine that something is out of focus before we can send directions to correct the focus. Focusing occurs by stimulating the smooth muscle of the ciliary body in the eye to contract, thereby enabling the lens to change its shape (accommodation). During accommodation not only does the lens focus but the pupil constricts, both smooth muscle actions mediated by parasympathetic components of CN3.

Cerebral cortex

Area 8 (voluntary conjugate gaze)

Areas 17,18,19 (involuntary conjugate following movements)

LEFT

LEFT

RIGHT

Pathways Conjugate Eye Movement

Medial longitudinal fasciculus

RIGHT

Fig. 37 The pathway for lateral conjugate gaze. PPRF — pontine paramedian reticular formation.

The syphilitic (Argyll-Robertson) pupil (also called the prostitute's pupil because it accommodates but does not react) constricts during accommodation, which is normal, but does not constrict to light. The lesion is considered to lie in the pretectal area of the superior colliculus (Fig. 36).

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