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Causes of Dry eye syndrome
The tear film consists of three layers, an inner wetting (surfactant) layer of mucin, a middle layer of salt water, and an outer oily layer. The oil slows evaporation and helps to maintain the continuity of the whole film. A deficiency in one or more of these layers can cause the condition of dry eye.
The mucin is secreted by tiny glands called goblet cells in the conjunctiva. The salt-water layer is secreted by many tiny accessory lacrimal glands, which are also in the conjunctiva. The oil layer is secreted by 16 to 20 glands in the eyelids called the meibomian glands. The main lacrimal glands are in the upper and outer part of the bony eye cavern and they are not necessary for the maintenance of the tear film. They produce tears during weeping or watering (lacrimation) from irritation.
Many conditions can interfere with the three sources of the tear film and lead to dry eye:
- Mucin deficiency occurs in vitamin A deficiency (xerophthalmia); in a very unpleasant allergic response to certain drugs, known as the Stevens–Johnson syndrome; in extensive trachoma (see article on Trachoma); or after chemical burns.
- Salt-water secretion deficiency occurs in various connective tissue disorders that close down small glands (Sjögren’s syndrome, systemic lupus erythematosus, scleroderma and Wegener’s granulomatosis).
- Oil-secretion abnormalities occur in chronic blepharitis.
Other causes of dry eye include:
- Radiation
- Low humidity
- Excessive air conditioning
- Infrequent blinking
- Abnormally protruding eyes
- Secretion-drying drugs such as atropine
- High atmospheric temperature
- Lid burns
- Over-correction of baggy lids
Some people’s eyes remain slightly open during sleep. This may lead to corneal drying
