The lens of the human eye is connected to the ciliary body of the ciliary muscle via so-called zonular fibers (suspensory apparatus of the lens). On the frontal side of the lens is the iris that consists of circular (inner ring) and radial (outer ring) muslce fibers. The round opening that is generated by this muscular ring is called pupil. Contraction of the dilator leads to mydriasis, contraction of the sphincter to miosis. The pupil diameter can be 8mm maximum, 1,5mm minimum (miosis). On average, it`s about 3mm.