The Conjunctiva and Tears

The portions of the eye that are normally visible in the palpebral fissures are the cornea and sclera. Because the cornea is transparent, what is seen on looking at the cornea is the underlying iris and the black opening in centre of the iris called the pupil. The sclera forms the white of the eye and its anterior portion is covered by a filmy, moist membrane called the conjunctiva.

The conjunctiva extends from the junction of the cornea and sclera (known as the limbus, Fig. 2) and terminates at the inner portion of the lid margin.

The conjunctiva that covers the eye itself is referred to as the bulbar conjunctiva, whereas the portion that lines the inner surface of the upper and lower lids is called the palpebral portion. The junctional bay created when the two portions of the conjunctiva meet is referred to as the fornix. The lower fornix can easily be viewed by depressing the lower lid.

(Fig. 4)  Tear film

The tear film is composed of three layers .

The outermost layer consists of a lipid or fatty layerand is extremely thin. It acts to prevent evaporation of the underlying aqueous (watery) layer.

The central aqueous layer contains dissolved salts as well as glucose, urea, proteins, and lysozyme. The third innermost layer is a very thin mucous layer lying just over the surface of the cornea. Tear film abnormalities may arise in association with a number of clinical problems in the aged and particular problems related to contact lenses.