When you blink, a film of tears spreads over the eye, making the surface smooth and clear. Sometimes people don’t produce enough tears or the right quality of tears to keep their eyes healthy and comfortable. This condition is known as dry eye.
The tear film consists of three layers:
- An oily layer
- A watery layer
- A layer of mucus
Each layer has its own purpose. The oily layer, produced by the meibomian glands, forms the outermost surface of the tear film. Its main purpose is to smooth the tear surface and reduce evaporation of tears.
The middle layer makes up most of what we ordinarily think of as tears. This watery layer, produced by the lacrimal glands in the eyelids, cleanses the eye and washes away foreign particles or irritants.
The inner layer consists of mucus produced by the conjunctiva. Mucus allows the watery layer to spread evenly over the surface of the eye and helps the eye remain moist. Without mucus, tears would not stick to the eye. Normally, the eye constantly bathes itself in tears. By producing tears at a slow and steady rate, the eye stays moist and comfortable.
Conditions that affect the lacrimal gland or its ducts – including hormonal changes associated with menopause and autoimmune diseases like lupus and rheumatoid arthritis – lead to decreased tear secretion and dry eye.
Tear secretion also may be reduced by certain conditions that decrease corneal sensation. Diseases such as diabetes and herpes zoster are associated with decreased corneal sensation, as is long-term contact lens wear and surgery that involves making incisions in or removing tissue from the cornea (such as LASIK).
Dry eye symptoms often include burning and scratchiness of the eyes and many people complain they can’t keep their eyes open long when they are reading, watching TV or when outside in the wind.
A wide variety of common medications, both prescription and over-the-counter, can cause dry eye by reducing tear secretion. Be sure to tell your ophthalmologist if you are using:
- Diuretics for high blood pressure
- Beta-blockers for heart or high blood pressure
- Antihistamines for allergies
- Sleeping pills
- Anti-anxiety medications
Additionally, exposure to dry windy climates, smoke, and blowing air contribute to dry eye symptoms.
Eyedrops, called artificial tears, are similar to your own tears. They lubricate the eyes and help maintain moisture. Artificial tears are available without a prescription. There are many brands on the market, so you may want to try several to find the one you like best.
Preservative-free eyedrops are available for people who are sensitive to the preservatives in artificial tears. If you need to use artificial tears more than every two hours, preservative-free brands may be better for you. You can use the preservative-free tears as often as necessary – once or twice a day or several times an hour.
Conserving your tears
Conserving your eyes’ own tears is another approach to keeping the eyes moist. Tears drain out of the eye through a small channel into the nose (which is why your nose runs when you cry). Your ophthalmologist may close those channels either temporarily or permanently with punctual plugs. This method conserves your own tears and makes artificial tears last longer.