Dry eye
What is it?
 |
| The normal tear film. Courtesy Allergan. |
Tears lubricate and smooth the front surface of the eye. Dry eye is a condition in which there are insuffient or poor quality tears.
Normal tears
The normal tear film is composed of 3 layers:
- The lipid layer is produced by the meibomian oil glands of the margins of the eyelid. The main function of this layer is to prevent evaporation of the tears.
- The aqueous, or watery, layer is produced mainly by the lacrimal gland which is located just inside the eye socket. This layer rinses away debris, and contains nutrients and antimicrobial agents that nourish the eye and protect it from harm.
- The mucin layer is produced by the surface of the eye. Mucin allows the watery components of the tears to 'wet' the surface of the eye.
Types of dry eye
There are two main types of dry eye.
- Secretive dry eye - inadequate tear producion
- Evaporative dry eye - adequate tear production but excess evaporation
Inadequate tear production
Some patients do not make enough tears. Many of these patients have inflammation in the tear (or lacrimal) gland and inflammation elsewhere in the body.
Diseases associated with reduced tear production include:
- Rheumatoid arthritis
- Sjogren's syndrome
Excessive tear evaporation
The surface of the eye is exposed to the air and thus to drying.
The commonest causes of increased evaporation of the tears are:
- Meibomian gland disease in which the oil glands of the eyelids fail to coat the surface of the tears with a healthy layer of oil.
- Abnormal eyelid position and reduced blinking
Dry eye symptoms
Patients with dry eyes suffer from a number of symptoms:
- Discomfort, usually described as dryness or burning
- Fluctuating or blurred vision
- Light sensitivity, known as photophobia
- Intolerance to dry conditions such as air conditioning
- Contact lens intolerance
- Reduced ability to perform near tasks such as reading and computer work
Who gets dry eye
Certain people are more likely to get dry eyes:
- Women
- Older patients
- Patients with autoimmune disease such as rheumatoid arthritis
- Those taking antihistamines, hormone replacement, acne therapy or oral contraceptives