Although the eye is commonly referred to as a globe, it is not really a true sphere. It is composed of two spheres with different radii, one set into the other.

The front, or anterior, sphere is the smaller and more curved of the two and is called the cornea. The cornea is the window of the eye since it is a completely transparent structure.

The posterior sphere is a white opaque fibrous structure called the sclera. The cornea and the sclera encase the eye and form a protective shell for all the delicate tissues within.

The eye measures approximately 24mm in all its main diameters in the normal adult.

'Vutest' analyses the various functions of the eyes to standards recognised by many ophthalmic authorities, and recommends that should any of the functions fall below a good standard, you are referred to an optometrist for expert advice.