these nuts
The lens. And apparently the cornea also. Please see What_part_of_the_eye_focuses_light_to_form_an_image_to_the_retina
for a more complete answer.
It is the lens. It is flexible because it is semi hard and if squeezed can be changed into different shapes.
Onto your retina. Onto your retina.
The lens bends the light rays to focus them on the retina.
The cornea and the lens focus the light on the retina - but the "image" you see is formed in the brain from just parts of the light image that exists in the eye.
Lens
The macula. It is the central area of the retina, where the lens forms the central part of an image. It contains a high density of cone type light sensitive receptors.
This process that produces a focused image on the retina through the bending of light rays is called refraction. To bring near and far objects into focus, it is necessary for the eye lens to make an adjustment through this process as light rays enter the retina.
retina
Lens, Cornea, Humerus focus light into the retina
Lens
Eyes are able to focus when the Ciliary muscles attached to the lens adjust itself. They adjust itself so that the curvature of the lens varies according to where the light rays are coming from, so that it hits the retina properly to form a clear image.
When bending light rays to focus them on the retina the two structure involved are the air-cornea interface which accounts for about two-thirds of the light-bending process and the lens which accounts for the remaining third but also makes the necessary adjustments to allow the eye to focus on objects at different distances.
Both the cornea (hard outer tissue) and the lens (farther inside) curve light rays that fall on the outer eye and direct them toward the retina. The lens is adjusted by muscles in the eye, while the cornea has a fixed focus.