Dry eyes can happen when tears evaporate too quickly, or if the eyes produce too few tears. It is common in humans and in some animals. It can affect one or both eyes, and it can lead to inflammation.
One study found that 17 percent of 2,127 patients visiting a hospital in Japan were diagnosed with dry eye, while 14.6 percent in a group of 2,520 older individuals reported symptoms of dry eyes.
Dry eye syndrome can occur at any age, and in people who are otherwise healthy. It is more common with older age, when the individual produces fewer tears. It is also more common in women than in men.
It is more common in places where malnutrition results in a vitamin A deficiency.
Dry eyes can become red and irritated.
The eyes produce tears all the time, not only when we yawn or experience emotion. Healthy eyes are constantly covered with a fluid, known as a tear film. It is designed to remain stable between each blink. This prevents the eyes from becoming dry and enables clear vision.
If the tear glands produce fewer tears, the tear film can become unstable. It can break down quickly, creating dry spots on the surface of the eyes.
Tears are made of water, fatty oils, protein, electrolytes, substances to fight off bacteria, and growth factors. The mixture helps keep the surface of the eyes smooth and clear, so that we can see properly.
Dry eyes can result from:
an imbalance in the tear mixture, so that it evaporates too fast
insufficient tear production for good eye health
Other causes include eyelid problems, some drugs, and environmental factors.
Imbalance in the tear mixture
The tear film has three layers, oil, water, and mucus. Problems with any of these can lead to dry eye symptoms.
The top layer, oil, comes from the edges of the eyelids, where the meibomian glands produce lipids, or fatty oils. The oil smooths the tear surface and slows down the rate of evaporation. Faulty oil levels can cause the tears to evaporate too quickly.
Inflammation along the edge of the eyelids, known as blepharitis, as well as rosacea and some other skin disorders, can cause the meibomian glands to become blocked, making dry eyes more likely.
The middle layer is the thickest, consisting of water and salt. The lacrimal glands, or tear glands, produce this layer. They cleanse the eyes and wash away particles and irritants.
Problems with this layer can lead to film instability. If the water layer is too thin, the oil and mucus layers may touch each other, resulting in a stringy discharge, a hallmark sign of dry eyes.
The inner layer, mucus, enables the tears to spread evenly over the eyes. A malfunction can lead to dry patches on the cornea, the front surface of the eye.
Reduced tear production
After the age of 40 years, tear production tends to fall. When it drops to a certain point, the eyes can become dry and easily irritated and inflamed. This is more common in women, and especially after the menopause, possibly due to hormonal changes.
Reduced tear production is also linked to:
autoimmune diseases, like Sjogren’s syndrome, lupus, scleroderma or rheumatoid arthritis
vitamin A deficiency
refractive eye surgeries, such as laser-assisted in-situ keratomileusis (LASIK), increase the chance of dry eyes, but the symptoms are usually temporary
Eyelid problems, medications, and environmental factors
Each time we blink, our eyelids spread a thin film of tears across the surface of the eyes.
Most people blink about five times a minute. Eyelid problems can affect the blinking motion that spreads the tear film evenly across the eyes.
Eyelid problems include ectropion, where the eyelid turns outward, or entropion, where it turns inward. Inflammation along the edge of the eyelids, known as blepharitis, may also cause dry eyes, as can contact lenses.
Medications that can cause dry eyes include:
angiotensin-converting enzyme (ACE) inhibitors
some sleeping pills
birth control pills
some acne drugs, specifically isotretinoin-type medications
morphine and other opiate-based painkillers
Climatic factors include a dry climate, sun, wind, and other types of hot blowing air or dry air, as in an airplane cabin.
High altitude, smoke, and the use of contact lenses are also risk factors.
Using a computer monitor, reading, or driving a vehicle, as the increased visual concentration may slow down the blinking rate, so that the eyes become dry.
Diseases that can lead to dry eyes include shingles, Bell’s palsy, and HIV infection.
A patient with dry eye syndrome may experience a range of symptoms, including:
a stinging or burning sensation, and a feeling of dryness, grittiness, and soreness in the eyes
a feeling like sand in the eye
stringy mucus in or around the eyes
eye sensitivity to smoke or wind
redness of the eyes
difficulty keeping the eyes open
eye fatigue after reading, even for a short time
blurred vision, especially towards the end of the day
sensitivity to light
discomfort when wearing contact lenses
eyelids sticking together when waking up
Some people find the pain very strong, and this can lead to frustration, anxiety, and difficulty functioning in daily life.
Complications may include a worsening of eye redness and light sensitivity, increasing painful eyes, and deterioration of eyesight.
A doctor will do a physical examination and ask the patient about symptoms, their medical history, any current medications, and about their occupation and personal circumstances.