Not a day goes by where I don't see at least one case of dry eyes. Most cases present as mild intermittent foreign body sensation accompanied by blurry vision. Others present as "tired eyes" at the end of the day or "sore eyes". In some cases, tearing can even be a sign of dry eyes.
That is counterintuitive until you understand how the tear glands work. There are lots of little glands throughout the conjunctiva, the clear skin that covers the surface of the eye. These glands are like a garden hose and produce a small amount of tears constantly to keep everything moist. If they don't make enough tears, the lacrimal gland, which sits just above the eye, turns on. It is like a fire hose and two settings: off and flood the eye with tears. This reflex tearing protects the eyes. The eyes water because they have been dry -- the tearing is your body's way of protecting your corneas from drying out.
The tear film does two things. First, it lubricates the eye so that the eyelid floats rather than rub against the surface of the eye. When the tear film is insufficient, the eyelid rubs against the cornea creating foreign body sensation or scratchiness. The brain doesn't always know how to interpret the signal from the nerve, so sometimes it can feel like something underneath the eyelid, can feel like a general soreness in the eye, and I've even heard it described as pain along the eyebrow or a headache on one side of the head. Second, the tear film smoothes out the surface of the eye. Imagine a lake on a perfectly calm day -- you can see a nice reflection in the water. As soon as ripples appear, the image disappears as well. It is the tear film that makes the surface of the eye perfectly smooth, creating a sharp image. Without a good tear film, vision is blurry.
Winter time is classically the worst time for dry eyes because the humidity is low and then we turn on the heater and dry out the air even more. With the unusual winter we are having this year, the plants are confused and staring to bloom, so there are more allergens in the air than normal. Allergies make the eyes dry both from the inflammation associated with the allergic reaction and from the anti-histamines we take for relief. Other medications can make the eyes dry as well. Certain medication conditions like rheumatoid arthritis or lupus can manifest as dry eyes. Corneal disorders, like Epithelial Basement Membrane Dystrophy (EBMD), or a previous corneal abrasion can predispose a person towards dry eyes. Spending a lot of time on the computer or reading for prolonged periods makes the eyes dry as well due to decreased blinking.
While "Dry Eyes" sounds like a minor problem, it can be a rather debilitating condition and often goes undiagnosed. Treatment can be as simple as lubricating the eyes with over-the-counter artificial tears, but could require medication or the placement of punctal plugs to increase the effectiveness of the tear film. A thorough history and complete eye exam to rule out a more serious condition is the first step.
More on dry eyes here.