Question #669

There are three distinct intrinsic eye muscles all consisting of smooth muscle:

1. Ciliary muscle – consists of fibres orientated either longitudinally, radially or circumferentially which contract during accommodation to increase the curvature of the lens. The muscle primarily receives parasympathetic innervation via the short ciliary nerves. Since these nerves also carry parasympathetic fibres to the sphincter pupillae muscle, accommodation is often associated with constriction of the pupil.
2. Dilator pupillae – dilates the pupil and is innervated by sympathetic fibres that may be carried via either the short ciliary or long ciliary nerves
3. Sphincter pupillae – constricts the pupil and is innervated by parasympathetic fibres via the short ciliary nerve.

To make things more complicated there is evidence that all three of the above muscles receive both sympathetic and parasympathetic innervations.

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