Fibers arranged in a circular pattern make up the sphincter pupillae muscle (Table 8.9), which is innervated by parasympathetics—contraction of its fibers decreases or constricts the pupillary opening.
Contractile fibers arranged in a radial pattern make up the dilator pupillae muscle, which is innervated by sympathetics—contraction of its fibers increases or dilates the pupillary opening.
Inner layer of the eyeball