The term dry eye relates to any form of tear dysfunction, whether it is caused by tear insufficiency where where there is an absolute lack in tear volume, or where any other component of the tear film is diminished. The tear film itself is composed of an outer oily or lipid layer which reduces evaporation and lubricates, a watery layer and finally a mucoid protein layer which acts as a wetting agent for the cornea. The symptoms of a dry eye are soreness, itching and surprisingly a watery eye caused where the irritation of the eyes caused by basal tear insufficiency causes reflex tearing of a much more watery tear which then causes further discomfort.
The Lipid Layer is secreted by the meibomian glands which open onto the inside of the upper and lower lid margins. This layer servers to lubricate the surface and reduce evaporation.
The Watery Wqueous Layer, which comprises the bulk of the tears is produced by the lacrimal gland, located above and behind the upper eye lid.
The Mucin Layer is secreted by the goblet cells which are scattered on the conjunctiva, lining the inner lid surface. This protein layer serves to serves as a wetting interface between the cornea and the aqueous layer.
If any one of these three tear components are out of balance it produces the symptoms known as a dry eye, causing sore red itchy and sometimes watery eyes; It can be quite difficult trying to explain to a patient that their watery eyes are actually dry!
It is important to remember that whilst there is no one perfect treatment, dry eyes are normally regarded as self limiting and non sight threatening
There are numerous drops and ointments available designed to supplement tears, some with mucolytics to reduce excessive mucus others with sodium hyalonurate which was originally isolated in cow eyes and is supposed to more closely mimic natural tears, then there are gels like lacrilube which are useful in keeping the eye moist during sleep but tend to cause smeary vision, if used during day time.
Tear dysfunction is often accompanied by other conditions such as blepharitis, which is a form of eczema of the eye lids and again there are different types of drops to reduce symptoms and improve lid hygiene, blephagel made by Thea is a new agent and seems to be particularly effective.
If using drops frequently become difficult or problematic punctum plugs may be indicated. These tiny plugs are inserted into the tear punctum ( the drainage channel at the nasal end of the lower lid) This reduces tear drainage and allows the natural tears to last longer. It is a good idea to have temporary plugs fitted first to assess the likely benefit. I have been fitting these plugs for many years with a good success rate.
Meibomian Gland Dysfunction Some times the symptoms of dry eye are produced by excess or faulty secretions from the meibomian glands which line the eye lids. There is an excellent clinical article on this at http://www.revoptom.com/content/c/15811/