How Do Tears Work?
When you blink, a film of tears spreads over the eye. This keeps the eye’s surface smooth and clear. The tear film is important for good vision.

The tear film is made of three layers:
= An oily layer
= A watery layer
= A mucus layer

Each layer of the tear film serves a purpose.
The oily layer is the outside of the tear film. It makes the tear surface smooth and keeps tears from drying up too quickly. This layer is made in the eye’s meibomian glands.

The watery layer is the middle of the tear film. It makes up most of what we see as tears. This layer cleans the eye, washing away particles that do not belong in the eye. This layer comes from the lacrimal glands in the eyelids.

The mucus layer is the inner layer of the tear film. This helps spread the watery layer over the eye’s surface, keeping it moist. Without mucus, tears would not stick to the eye. Mucus is made in the conjunctiva. This is the clear tissue covering the white of your eye and inside your eyelids.

Normally, our eyes constantly make tears to stay moist. If our eyes are irritated, or we cry, our eyes make a lot of tears. But, sometimes the eyes don’t make enough tears or something affects one or more layers of the tear film. In those cases, we end up with dry eyes.

Dry Eye Causes
People tend to make fewer tears as they get older due to hormonal changes. Both men and women can get dry eye. However, it is more common in women—especially those who have gone through menopause.
Here are some other causes of dry eye.
= Certain diseases, such as rheumatoid arthritis, Sjögren’s syndrome, thyroid disease, and lupus
= Blepharitis (when eyelids are swollen or red)
= Entropion (when eyelids turn in); ectropion (eyelids turn outward)
= Being in smoke, wind or a very dry climate
= Looking at a computer screen for a long time, reading and other activities that reduce blinking
= Using contact lenses for a long time
= Having refractive eye surgery, such as LASIK
= Taking certain medicines, such as:
      - Diuretics (water pills) for high blood pressure
      - Beta-blockers, for heart problems or high blood pressure
      - Allergy and cold medicines (antihistamines)
      - Sleeping pills
      - Anxiety and antidepressant medicines
      - Heartburn medicines

How Is Dry Eye Diagnosed?
Your ophthalmologist will begin with an eye exam. He or she will look at your eyelids and the surface of the eye. They will also check how you blink.
There are many different tests that help diagnose dry eyes. Your ophthalmologist may do a test that measures the quality or the thickness of your tears. He or she may also measure how quickly you produce tears.

How Is Dry Eye Treated?
= Adding Tears
      - Your ophthalmologist might tell you to use artificial tears. These are eye drops that are like your own tears. You can use artificial tears as often as you need to. You can buy artificial tears without a prescription. There are many brands. Try a few until you find a brand that works best for you.   
      - If you use artificial tears more than six times a day or are allergic to preservatives, you should use preservative-free tears. This is because if the tears with preservatives are used a lot, these chemicals may start to irritate your eyes.
      - If you use artificial tears more than six times a day or are allergic to preservatives, you should use preservative-free tears. This is because if the tears with preservatives are used a lot, these chemicals may start to irritate your eyes.

= Saving Tears
      - Your ophthalmologist may suggest blocking your tear ducts. This makes your natural tears stay in your eyes longer. Tiny silicone or gel plugs (called punctal plugs) may be inserted in your tear ducts. These plugs can be removed later as needed. Your ophthalmologist could also recommend surgery that permanently closes your tear ducts.