Pupil

If we assimilate the eye, in its structure, to a camera, the pupil is the amount of diaphragm. As described in ' iris, this anatomical structure has two muscles (the pupillary sphincter and dilator) that with their contraction are able to vary and adjust the “forum” pupil through which light rays enter the eye going to end up on the retina in relationship to the amount of ambient light or to reduce the depth of field as in reading. The pupil is therefore in continuous movement by passing 1,5 -2 mm (miosi that is realized for action on mesencephalic parasympathetic nervous constrictor muscle of the pupil), who is a 8-9 mm (midriasi which is determined by the action of nerve fibers of the sympathetic nervous system that reach the dilator muscle of the pupil). The changes in pupil diameter, which are of fundamental importance in the refractive surgery, essentially depend on the ambient light, with respect to one “state pupillary” characteristic for each of us to prevalence of sympathetic or parasympathetic. Other factors can influence the dynamics of pupillary (defect of view, emotional state, stress situations, fatigue, drugs taken, etc.) or inflammatory (iriti, iridocyclitis, glaucoma Acuto).