As we saw a moment ago, the inner eyelids and the front of the eyeball are covered with a fine transparent membrane called the conjunctiva. The space between the eyelids and the eyeball is the conjunctival sac.

Behind the conjunctiva is the cornea, a clear, transparent membrane.

The space between the lens and the cornea is divided into two parts by the iris. The part in front of the iris is known as the anterior chamber; the part between the iris and the lens is the posterior chamber.

The anterior and posterior chambers are filled with a clear watery fluid - the aqueous humour - that helps to maintain the slight forward curve of the cornea. The aqueous humour is produced by the ciliary body.