What are tears?
Tears form a protective film over the surface of the eye and help lubricate the eye surface and clear the eye of any particles of dust or debris. Tears are composed of three distinct layers, an inner mucous layer that allows the tear to stick to the eye, a watery mid layer that provides moisture, oxygen and nutrients to the cornea, and a lipid top layer that provides an oily surface to help prevent evaporation.
The watery middle layer of tears is produced by the lachrymal glands that lie above the eye. The lipid layer is produced by glands in the eyelid. Tears enter the eye through a small opening in the corner of each eye.
What causes dry eye?
Dry eyes can have several causes:
- Reduced tear production due to inflammation associated with a chronic eye disease called keratoconjunctivitis sicca, or dry eye disease in which the eye does not produce sufficient tears to cover the cornea and protect the surface of the eye.
- An abnormality in the composition of tears with insufficient production of the lipid layer, causing more rapid evaporation. This is common as part of the natural aging process.
- A side effect of some medications, such as isotretinoin and antihistamines.
- A symptom of certain diseases, such as rheumatoid arthritis and diabetes.
- Infrequent blinking such as when staring at the computer screen.
- Wearing contact lenses.
Treatments for dry eyes
When tear production is reduced, the eye becomes inflamed and this reduces tear production further. Cyclosporine, a medication that is used systemically to suppress the immune system, also reduces inflammation in the eye and has been found to be effective at increasing natural tear production. Cyclosporine containing eye drops are used to treat dry eye disorders.