Focusing of the eye. Artwork of a section through the eye showing different states of focus. The cornea is at left (blue), the lens (white) is at centre and the ciliary body is at right Attached to the ciliary body (brown) are small fibres (white), known as zonular fibres, which hold the lens in place. The lens focuses images on the retina. The ciliary body contains muscle fibres. When the ciliary body contracts the zonular fibres relax and the lens thickens, enabling it to focus on near objects (bottom half of image). When the ciliary body relaxes the zonular fibres contract and the lens thins, enabling it to focus on distant objects (top of image).