The Definitive Source for Dry Eye Information on the Internet
Dry eye is a group of conditions each characterized by loss of water from the tear film sufficient to increase the amount of salt relative to the amount of water. As a result, the tear film becomes too concentrated, and as it does, its "osmolarity" increases. I think most of us will remember "osmosis" from our high school chemistry class. Well, that's what happens in dry eye--when the tear film becomes more concentrated it pulls water out of the surface of the eye, making it dry.
If you have dry eye you experience sandy-gritty irritation or burning in your eyes that generally gets worse as the day goes on.
There are two basic ways that someone can get dry eye--decreased tear production or increased tear film evaporation. Tear production can go down from conditions like rheumatoid arthritis or Sjögren's syndrome, or from any condition that decreases sensation on the surface of the eye--things like diabetes, long-term contact lens wear, corneal surgery, LASIK, trauma to the 5th nerve and certain viruses.
Tear evaporation can increase from long-standing eyelid inflammation or blepharitis, or from simply having large eyes (i.e. as in, "my you have big beautiful eyes"), or from thyroid eye disease. Blepharitis (specifically posterior blepharitis) may be associated with ocular rosacea, and the inflammation causes sandy-gritty eye irritation that is worse in the morning. Long-standing posterior blepharitis results in decreased function of the oil glands in the eyelid. This is important because the oil produced by these glands enter the tear film and coat it, retarding evaporation like a biological Saran Wrap. With large eyes and with thyroid eye disease the eye surface area exposed to air increases, and evaporation is directly proportional to surface area.
There is now evidence that omega-3 essential fatty acids in the diet (present in salmon, sardines, herring and mackerel) are helpful in not only suppressing the inflammation of rheumatoid arthritis, but also in suppressing the inflammation of blepharitis and the inflammation of the tear gland that causes decreased tear production in Sjögren's syndrome. In addition, it has been found that these same omega-3 essential fatty acids are used by the oil glands in the eyelid to make a healthy tear film oil layer.
One of the most important and early changes that occurs in dry eye is a reduction in the number of conjunctival goblet cells on the surface of the eye. You're probably wondering what a conjunctival goblet cell is. Did you ever wonder why your eyes don't squeak when you blink?
It's because on the surface of the eye there are thousands of mucous-containing cells called "goblet cells." Mucous is the most slippery substance in the human body. Think of these goblet cells as the "ball bearings" of the eye surface--instead of containing stainless steel they contain mucous. And this is why normal eyes don't squeak when they blink, and one of the reasons why dry eyes are so uncomfortable.
Another early change that occurs in dry eye a loss of corneal glycogen. All you need to know about glycogen is that it is the energy source for corneal wound healing. As corneal glycogen gets depleted it can be harder and harder for dry eyes to heal.
Finally, and in much more advanced disease, as water gets pulled by osmosis across the cornea, corneal cells peel off and tear film instability develops and dry spots appear.
Symptoms are the best way to know if you have dry eye and it is always important to have the diagnosis confirmed by an eye doctor. He will also be able tell you why you have dry eye and place you on the best treatment program. It used to be that all artificial tear solutions were the same and patients would pick their brand almost like some people pick their car color! These solutions were designed to cover up dry spots and were developed before it was realized that dry spots are the result of dry eye, rather than the cause.
Recently it was discovered that just like the electrolytes or salts in the blood are biologically active, the electrolytes in the tears are biologically active as well. There is now an eye drop for dry eye called TheraTears that rehydrates the tear film, lowering elevated tear film osmolarity, and provides the tear film electrolytes that are crucial for growth, maintenance and repair of the eye surface. In peer-reviewed studies TheraTears has been shown to provide cumulative dry eye relief by promoting healing of the eye surface as evidenced by restoration of the goblet cells and glycogen that have been lost in dry eye. Even more recently it has been found that dry eye can be helped by daily dietary supplementation of omega-3 essential fatty acids using TheraTears Nutrition (Omega-3 supplement with flaxseed and fish oils and vitamin E). If medical treatment is not adequate, dry eye can also be helped by the insertion of 'punctal plugs" designed to block tear drainage from the eye.
This site was last updated 06/13/08