You can have one type of dry eye. You can also have both at the same time.
When Your Eyes Don't Make Enough Tears
You may hear this called aqueous tear-deficient dry eye. A gland in the corner of your eye called your lacrimal gland makes your tears. Normally, this gland makes enough moisture to keep your eye healthy. Tears wash away dust and anything else that may fall in. They also protect your peepers from germs and infection.
When your lacrimal gland doesn’t make enough tears, it causes dry eye. Another name for this type is keratoconjunctivitis sicca. You might have it because your eyes have aged and aren’t able to make tears the way they used to.
You might also have it because of a medical condition, like:
- Rheumatoid arthritis
- Sjogren’s syndrome
- Thyroid disorders
- Vitamin A deficiency
You may also get this as a side effect of a medicine, like:
- Hormone replacement therapy
- Blood pressure medication
- Acne medicine
- Birth control
- Parkinson's disease meds
Sometimes, lacrimal glands can have trouble making enough tears after laser surgery. This usually goes away after a few months. You can also get this type of dry eye if inflammation or radiation damages your lacrimal glands.
When Your Tears Don't Stick Around Long Enough
When your tears dry up too quickly to help protect your eyes, you have something your doctor may call evaporative dry eye. Sometimes it happens because of a problem with the makeup of your tears. Other times, it comes from changes to your eye, or the environment.
Tears have three layers: an oily outer, a watery middle, and an inner mucus layer. The oily outer layer helps keep the watery middle from evaporating too quickly. The mucus one spreads tears evenly over the surface of your eye. A problem with any of these can cause dry eye.
Glands inside your eyelids called meibomian glands make the oil in your tears. Sometimes they get clogged. When that happens, your tears don’t get enough oil. The watery layer of your tears loses its protection, and your tears evaporate.
Sometimes, dry eye happens because you can't keep moisture in your eye long enough. Tears don't dry up. They just leave.
Reasons for this include:
- Things in the environment like wind, smoke, or dry air
- Not blinking enough, as may happen when you’re staring at a screen or reading
- Eyelid problems like ectropion (your eyelids turn outward) or entropion (your eyelids turn inward)
If the exposed surface of your eye gets bigger, your tears may have a hard time covering it. This can happen if you have thyroid issues that make your eyes bulge, or if you have eye surgery that opens your eye too far.