This limb includes Edinger-Westphal nucleus and the oculomotor neurons.
The main function of the Edinger-Westphal nucleus is to send axons in the oculomotor nerve to control the ciliary ganglion which in turn, sends its axons in the short ciliary nerve to control the iris and the ciliary muscle of the eye.
The reflex, controlled by the parasympathetic nervous system, involves three responses: pupil constriction, lens accommodation, and convergence.
A near object (for example, a computer screen) appears large in the field of vision, and the eye receives light from wide angles.
The refractive power mainly resides in the cornea, but the overall refractive power is achieved by the actual lens changing its shape.
Information from the light on each retina is taken to the occipital lobe via the optic nerve and optic radiation (after a synapse in the lateral geniculate body of the posterior thalamus), where it is interpreted as vision.The suspensory zonules of Zinn relax and the radial tension around the lens is released.This causes the lens to form a more spherical shape achieving a higher level of refractive power.The refractive index of the eye’s lens system allows the eye to produce sharply focused images.
For example, geometrical optics show that as a distant object is brought closer to the eye, the focus of the object becomes blurrier in the plane behind the retina; however, as a result of the increase in the refractive power of the eye, this image becomes clear.
The change in the shape of the lens is controlled by the ciliary muscles inside the eye.