Dry eyes can happen when tears evaporate too quickly, or 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 elderly 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.
Signs and symptoms
Dry eyes can become red and irritated.
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
- Double vision
- Eyelids stick together when waking up
Complications may include a worsening of eye redness and light sensitivity, increasing painful eyes, and deterioration of eyesight.
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.
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
- Radiation treatment
- 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:
- Some diuretics
- Angiotensin-converting enzyme (ACE) inhibitors
- Some sleeping pills
- Birth control pills
- Some antidepressants
- 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.
Treatment and tips
A doctor will do a physical examination and ask the patient about symptoms, their medical history, any current medications, and information about their occupation and personal circumstances.
The type of eye drops to use depend on the cause of the dry eye.
Tests can reveal the quantity of tears behind the eyelid, whether the tear film is functioning properly, and the rate of evaporation.
Treatment aims to keep the eyes well lubricated, but the approach depends on the underlying cause.
Three ways of keeping the eyes lubricated are:
If the problem stems from an ophthalmic or systemic condition, such as an eye infection or psoriasis, the underlying condition needs to be treated first.
Using natural tears
Tips for making the most of natural tears include:
Artificial tears and eye drops
Artificial tear or eye drops, available over the counter, can help to lubricate mildly dry eyes. A doctor can advise which ones to use.
Eye drops without preservatives can be used as often as necessary, but those with a preservative usually have a maximum safe dosage of four times a day.
Eye drops for removing redness should not be used.
It can be helpful to apply eye drops before doing activities that tend to exacerbate dry eye symptoms. Ointments are better for night time use, because they may blur vision.
If the patient has blepharitis, they may need to clean the affected area regularly with a dilute solution of baby shampoo. The doctor may prescribe antibiotic drops or ointment for night time use. Sometimes, an oral antibiotic, such as tetracycline or doxycycline, is used.
Steroid drops may help reduce inflammation if symptoms remain severe, even after the frequent use of eyedrops.
Eyelid problems, such as an incomplete blink, may be treated by an oculoplastic surgeon, who specializes in eyelid problems.
Reducing tear drainage
In more severe cases, tear ducts, which drain away the tears, may be deliberately blocked, partially or completely, to conserve tears. Silicone plugs can be placed in the tear ducts to block them. This helps keep both natural and artificial tears on the eyes for longer.
Eye surgery can correct some problems that lead to dry eye.
A surgeon can shrink the tissues of the drainage area by using a heated wire in a minor operation known as thermal cautery.
A Boston Scleral Lens is a contact lens that rests on the sclera, the white part of the eye. It creates a fluid-filled layer over the cornea, preventing it from drying out.
Medications for patients with chronic dry eyes include cyclosporine eye drops, or Restasis. Cyclosporine reduces eye-surface inflammation and triggers increased production of tears. Patients should not use this drug if they have an eye infection or a history of herpes viral infection of the eye.
Some studies indicate that omega-3 and omega-6 fatty acids may help reduce the risk or the incidence of dry eyes. However, there are not enough large-scale research studies in humans to support their use as primary treatment.
Some patients benefit from wearing moisture-chamber spectacles, which wrap around the eyes like goggles. The spectacles help retain moisture in the eyes and protect them from wind and other irritants. New, sporty designs have increased their popularity.
Salivary gland transplantation is a surgical procedure that is occasionally considered in persistent and severe cases that have not responded to other treatments.
Some of the salivary glands are removed from the lower lip and grafted, or placed into the side of the eyes. The saliva they produce becomes a substitute for tears.
Tips for caring for dry eyes
There are some ways of reducing the symptoms of dry eyes:
- Clean the eyelids by gently wiping the eyes with a piece of cotton wool dipped in warm water, to reduce the likelihood of them becoming inflamed
- Gently massage the eyelid in a circular motion, using a clean finger, to help remove mucus from the eyelid glands
- A diet rich in omega-3 fatty acids may help prevent dry eye syndrome. Sources include oily fish, canola oil, walnuts, flax oil, ground flax seed, hemp oil, hemp seed, olive oil, pumpkin seeds, and soybeans
Dry eye can lead to watery eye, as a different kind of tear tries to compensate.
Most people with mild dry eye syndrome have no long-term problems or complications, but severe symptoms can lead to eye inflammation, infection, and damage to the surface of the cornea.
This damage can lead to ulceration or scarring, which can be painful and affect the patient's vision.
Conjunctivitis caused by dry eye does not normally require treatment, but if it is severe, long-lasting, or recurring, the patient should seek medical help.
Some people with dry eye syndrome sometimes have constantly watery eyes because they produce too many tears.
There are two types of tears, one that maintains the tear film and one that helps wash away dirt and foreign particles.
As a reaction to the irritation, people with dry eyes may produce more of the kind of tears that wash away dirt. This can lead to watery eyes.