Answer
Adjustment of the lens to see an object closer to the eye is called visual accommodation. To see a near object the lens must become rounder and thicker.
Convergence is the medial rotation of the eyeballs by the medial rectus muscles so that each eyeball is directed towards the near object being viewed.
Focusing is the combined bending of light rays by cornea , lens, and eye humors so that the rays converge and form an image on the retina.
Constriction:(Pupillary) is reduction of the size of the pupils.
The sphincter pupillary muscles of the iris ( intrinsic eye muscles) enhance the effect of accommodation by decreasing the size of the pupil. This reflex is mediated by the parasympathetic fibers of the oculo-motor nerve (CN III). The process excludes the most divergent rays from the object being viewed from entering the eye for they would result in blurred vision/images.
Work Step by Step
The shape of the lens is controlled by ciliary muscles within the ciliary body.
In close vision, the ciliary muscles contract ; this releases the tension on the suspensory ligament which causes the lens to assume a rounder thicker shape because of its natural elasticity. this change of the shape of the lens bring the image to focus on the retina.
In distant vision, the the ciliary muscles relax and the suspensory ligament attached to the ciliary body tenses.This puts tension on the lens and it remains flat.
The function of convergence is to keep the object focused on the foveas of the retinas.
In viewing a distant object both eyes are directed straight ahead or are turned to one side --to the same degree. However, in visual fixation on a close object, both eyes converge-- the eyeballs rotate medially so that each each eye is directed to wards the object being viewed. Convergence is achieved by the contraction of the medial rectus muscles which are under the control of the somatic fibers of the oculo-motor nerve (CN III).
