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.
Horizontal cells interconnect groups of photoreceptor cells.
Amacrine cells interconnect groups of ganglion cells and bipolar cells. They are unusual neurons because they have no true axon. Ganglion cells possess long axons that extend through the nerve fiber layer of the retina and then come together to form the optic nerve. The retina possesses a number of histological layers, which are listed below along with their composition. They are listed in order moving from the outside of the eye towards the interior of the eye.