Dry eye is associated with aging, diabetes, rheumatoid arthritis, long-term contact lens wear, LASIK eye surgery, long-standing blepharitis and a relative dietary
deficiency of omega-3 essential fatty acids.

The tear film consists of three layers:

1. A water layer produced by the lacrimal gland. Did you ever wonder why your eyes have tears? It’s because the delicate living cells on the surface of the eye have no blood supply — they have a tear supply instead. So rather than getting important things like oxygen and electrolytes (special salts) from the blood, the eye surface gets them from the water layer of your tears. When the lacrimal gland does not produce enough tears, you develop dry eyes.

2. An oil layer produced by oil glands in the eyelid margin. This layer helps
protect the water layer from evaporation. Without an oil layer the tears evaporate too quickly and become too salty, producing dry eye.

3. A mucus layer directly on the eye surface that provides natural lubrication. If you don’t produce enough tears, or if your tears evaporate too rapidly, the resulting high salt concentration in the tear film decreases this layer, contributing to the symptoms of dry eye.

There are two general ways that someone can get dry eyes — decreased tear production or increased tear evaporation.

Production can go down from conditions such as 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 and certain viruses.

Evaporation can increase from long-standing eyelid inflammation of the oil glands in the eyelid or blepharitis, from simply having large eyes, or from thyroid eye disease.