Lens fibers at the periphery of the lens still possess their nuclei. The lens fibers are tightly coupled by surface interdigitations and many gap junctions. New lens fibers are added gradually throughout life. The iris functions to regulate the size of the pupil and hence the amount of light entering the eye. The iris contains two of the three intrinsic muscles of the eye.
Accommodation is a change in the focal length of the lens which occurs when viewing close objects.
The focal length of the lens is changed by changing the shape of the lens , not by moving the position of the lens. The shape of the lens is changed by changing the amount of tension on the lens. When the ciliary muscle contracts, the ciliary body changes shape and bulges out slightly towards the lens which reduces the tension of the ciliary zonule fibers and hence on the lateral margins of the lens. The Retina is the site of sensory transduction. Cone photoreceptor cells are specialized for sensing bright light and for color vision.