The Dry Eye

A patient might complain of dryness of the eyes simply because the conjunctiva is inflamed, but when the tear film really is defective, the patient might complain of soreness and irritation rather than dryness. The diagnosis of a dry eye depends on a careful examination and it is quite erroneous to assume that the tear film is inadequate simply because the patient complains of dryness, or even if the symptoms appear to be improved by artificial tears.

The normal tear film consists of three layers and the integrity of this film is essential for comfort and more importantly for good vision. The anterior, or outermost, layer is formed by the oily secretion of the meibomian glands and the layer next to the cornea is mucinous to allow proper wetting by the watery component of the tears, which lies sandwiched between the two. This three-layered film is constantly maintained by the act of blinking.

Causes

• Systemic disease with lacrimal gland
involvement:
– sarcoidosis
– rheumatoid arthritis (Sjögren’s
syndrome).
• Trachoma (chlamydial conjunctivitis and
keratitis – see next chapter).
• Neuroparalytic keratitis.
• Exposure keratitis.
• Old age.
• Other rare causes.

Signs

Slit-lamp Examination
In a normal subject, the tear film is evident as a rim of fluid along the lid margin and a deficiency of this can be seen by direct examination. Prolonged deficiency of tears can be associated with the presence of filaments – microscopic strands of mucus and epithelial cells, which stain with Rose Bengal. Punctate staining of the corneal epithelium is also seen after applying a drop of fluorescein. In some dry eye syndromes, for example, ocular pemphigoid and Stevens–Johnson syndrome, keratinisation of the cornea and conjunctiva with the formation of contracting adhesions between the opposed surfaces of the conjunctiva occurs. A similar change is apparent following chemical or thermal burns of the eyes.
Schirmer’s Test
One end of a special filter paper strip is placed between the globe and the lower eyelid. The other end projects forward and the time taken for the tears to wet the projecting strip is measured. The test is not an accurate measure of tear secretion but it provides a useful guide
Tear Film Break-up Time
Using the slit-lamp microscope, the time for the tear film to break up when the patient stops blinking is measured. This test is sometimes used as an index of mucin deficiency.

Management of the Dry Eye

This, of course, depends on the cause of the dry eye and the underlying systemic cause might require treatment in the first place. Artificial tear drops are a mainstay in treatment and various types are available, their use depending on which component of the tear film is defective. In severe cases, it might be necessary to consider temporary or permanent occlusion of the lacrimal puncta.