Iris dilator muscle the superior orbital fissure. From there, they travel with the nasociliary nerve and then the long ciliary nerve. They then pierce the sclera, travel between sclera and choroid to reach the iris dilator muscle. They will also pass through ciliary ganglion and travel in short ciliary nerves to reach the iris dilator muscle. The pupillary dilator acts to increase the size of the pupil to allow more light to enter the eye. It works in opposition to the pupillary constrictor. Pupil dilation occurs when there is insufficient light for the normal function of the eye, and during heightened sympathetic activity,
Ciliary muscle of the ring of ciliary muscle (causing constriction of the pupil and accommodation). The zonule fibers relax and the lens becomes more spherical, increasing its power to refract light for near vision. The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book. The ciliary fibers have circular (Ivanoff), longitudinal (meridional) and radial orientations. According to Hermann von Helmholtz's theory, the circular ciliary muscle fibers affect zonular fibers in the eye (fibers that suspend the lens in position during accommodation), enabling changes in lens shape for light focusing. When the