Structure of the eye

The eyeball itself is protected within the orbit (bony eye socket) by the eyelids, which blink automatically to spread a tear film over the surface of the eye and by the eyelashes, which sweep dust and particles away. It is also protected from trauma by the orbital bones.

The surface of the eyeball, that is, the clear cornea and the sclera (the tough, white outer coating of the eyeball) is protected in various ways. The cornea is very sensitive to touch and pain and the eye will reflexly blink if it is approached or touched. The sclera is protected by the conjunctiva, a thin membrane covering the sclera up to the corneal edge and is reflected back onto the entire inner edge of the eyelids. Between the conjunctiva and sclera, the Tenon’s Capsule (the connective tissue enveloping the posterior eyeball) prevents superficial infections (e.g. conjunctivitis) from spreading to the deeper structures.

Tears, which keep the eye moist, wash away particles and have antibacterial properties. The salty tear fluid is produced by the lacrimal glands, mucus- producing cells in the conjunctiva and small glands in the eyelids, which produce an oily substance that also add to the protective and lubricating nature of tears.

The eye itself is divided into -:

• The anterior chamber - extending from the inside of the cornea, to the front surface of the iris. This is filled with a fluid called aqueous humour, as is the small space between the iris and the lens, known as the posterior chamber.
• The posterior segment - extending from the back of the lens to the retina, and is filled with vitreous humour, which is thick and jelly- like and keeps the eyeball firm.