Each eyeball is roughly spherical, about 2.5 cm (1 in) in diameter, and lies in a protective bony socket in the skull. The eyeball has a tough outer coat called the sclera that maintains its shape. The choroid, which supplies the eye with nutrients, lies inside the sclera. The innermost layer, the retina, contains two types of light-sensitive cells: rods, which respond to dim light; and cones, which detect colour.
View of the retina
Blood vessels and nerve fibres leave the retina via an area called the optic disc. The area of the retina responsible for the most detailed vision is the macula.
Front of the eye
The ciliary body, and other delicate structures at the front of the eye, can be seen in detail in this magnified image. The ciliary body alters the shape of the eye’s lens so that light from either near or distant objects can be focused correctly.
This highly magnified view shows the precise arrangement of the fibre-like cells that make up the lens. The cells have no nuclei; this feature helps to make the lens transparent.