Dry eye is most common eye problem in North America. People with dry eye have burning, gritty or tired eyes. Dry eye occurs when the eye is bathed by not enough or poor-quality tears. Computer users and post-menopausal women are most often affected. Fortunately, this condition is often preventable and may be easily treated.
What is dry eye?
On average, people blink about 15 times per minute. When that rate slows, the eyes feel gritty, burning or tired, and become red. The eye’s protective coating of tears dries up, leaving the eye open to infection and injury. This condition is known as dry eye.
Not enough blinking is only one cause of dry eye – the leading eye problem in North America. About 10 million Americans have this condition. Dry eye is more common in women, especially after menopause. About 60% of eye fatigue is caused by dry eye.
Tears bathe and soothe the eye. They are important for eye health and clear vision. Dry eye occurs when tear quality is poor or not enough tears are available to protect the eye’s surface.
People with dry eye find it difficult to wear contact lenses. They may even produce fewer tears when they cry. When dry eye is serious, people may become sensitive to light or have blurry vision.
Without a protective layer of tears, the eye’s surface is easily scratched and is vulnerable to infection. Fortunately, your eye doctor can suggest many options to treat dry eye. With proper care, people with dry eye can avoid eye injury and vision loss.
Detecting dry eye
To detect dry eye, an eye doctor usually does a few simple tests during the annual eye exam.
Some eye doctors use a fluorescein test. They put a droplet of yellow dye into the eye, then count the number of seconds it takes for the tear film to break up. If it takes less than 10 seconds, the person has dry eye. Sometimes, the yellow dye will temporarily stain the eye. Viewed through a slit-lamp microscope, dry eye looks like dry, cracked skin.
The rose bengal test uses a reddish-purple dye to detect dry eye. During the Schirmer test, the eye doctor touches a strip of filter paper to the inner eyelid. The paper is used to measure tear production.
Some people are more likely to have dry eye. Computer users, who blink less often than normal (4 versus 15 blinks per minute on average), are often bothered by dry eye. More women than men are affected. People with allergies and contact lens wearers are more likely to develop this condition.
Tears are essential for healthy eyes and clear vision. Faulty eye mechanics (not enough blinking while reading or working on a computer) or the environment (dry air, wind, dust or sun) can dry tears before they are naturally replenished.
Some people are unable to make enough tears to protect the eye. In others, the eye’s natural recipe for tears may be missing a few important ingredients.
As people age, the eyes naturally produce fewer tears. About 75% of people over 65 have dry eye. Menopause, which affects the body’s estrogen levels, may cause dry eye.
Health problems, such as arthritis, can also affect tears. About 3 million American have dry eye because of Sjogren’s syndrome. This immune disorder affects the lacrimal glands, which make tears.
Some drugs — oral contraceptives, antibiotics, diuretics, antihistamines, antidiarrheals, anti-acne, antihypertensives and antidepressants — can interfere with tear production.
On the job, chemical or heat exposure may lead to dry eye.
Facial shape, eyelid disorders or contours on the eye’s surface can affect tear coverage. Some eye diseases can desensitize the eye’s surface and lead to a drop in tear production.
In all of these examples, tears are no longer there to wash and soothe the eye. Either the quality or number of tears is not good enough to protect the eye’s surface.
With proper care and treatment, people with dry eye can avoid discomfort, infections and eye injury.
Replace the tears
In most cases, the solution for dry eye is artificial tears. They are sold over the counter in most pharmacies. Artificial tears differ from drops that remove redness, which are not recommended for dry eye. Moisturizing ointments, often applied at bedtime, are sometimes prescribed by eye doctors.
Artificial tears add volume — allowing tears to rinse away microorganisms and grit, which can infect or scratch the eye’s surface. Most artificial tear products are used three to four times daily. Unpreserved artificial tears are used as needed — without restrictions. If too thin, artificial tears won’t last long. If too thick, they blur vision. Since not all artificial tears are the same, people may need to try a few brands before finding one that suits them. These products are the first line of defense against mild to moderate dry eye.
Plug the eye’s drain
The punctum is the opening of the eye’s drain. The eye has two drains – in the upper and lower corners of the eyelid margins near the nose. When the eyelid is gently pulled down, these tiny holes are exposed.
Blinking creates a vacuum that sucks tears down these drains. From there, they travel through nasolacrimal ducts to the throat. Post-nasal drip, a chronic cough or congested sinuses are signs that tears are overflowing this drainage system — a common problem in dry eye.
Tiny silicone plugs can block the punctal drains. They are inserted manually by an eye doctor, usually in the lower punctum to prevent gravity from draining tears away. When blocked, up to 88% less tears drain from the eye. This painless procedure takes just a few minutes. Once in place, people can’t see or feel the plugs at all.
Collagen plugs dissolve in 4 to 7 days. A temporary solution, they help eye doctors find out if plugging the punctum will prevent dry eye.
Plugs may be helpful if the dry-eye problem is in the watery middle layer of tears. Since plugs cost a few hundred dollars, they are usually used for moderate to severe dry eye.
Sealing the drain
Heat can permanently seal the punctum, blocking tear drainage. During thermal cautery, the eye doctor applies an anesthetic, then inserts the hot wire tip of the cautery device into the punctum. The tip is slowly withdrawn. Some scarring may occur. This procedure is not reversible.
A laser can seal the punctum, but this operation is expensive — over US$1,000. There is less scarring, but 20% of drains spontaneously reopen.
Before reaching for a medical solution to dry eye, your eye doctor may suggest a few simple steps.
Blink more often
Think of a blink as the eye’s windshield washer. People normally blink 15 to 18 times per minute. Computer users average only 3 to 4 times per minute! No wonder their eyes are dry!
Massage the eyelids
Place a warm washcloth over closed eyes. Gently massage the upper eyelid against the upper bone for 5 to 10 seconds. Massage the lower eyelid against the lower bone for the same amount of time. A daily eyelid massage stimulates stagnant tear-producing glands under the eyelids, renewing tear quality.
Diet plays a role
Natural diuretics — coffee, tea, cola, alcohol, chocolate — may play a role in promoting dry eye. Drink at least eight glasses of water daily.
Adjust dosages of certain drugs
Dry eye may be a drug-related side effect. Lowering the dosage of medication may solve the problem.
Control the environment
Investing in a humidifier at home or work, switching from fluorescent to incandescent lighting, turning down the thermostat or cutting down exposure to smoke or allergens may prevent dry eye.
Contact lens cleaning
When not cleansed or wetted properly, contact lenses can wick tears away from the eye’s surface. Lens-cleaning products without preservatives may be gentler on dry eyes.
With every blink, tears bathe the eye. They wash away dust and microorganisms that may cause infection or scratch the eye’s surface.
Tears have three layers: an oily outer layer, a watery middle layer and a mucousy inner layer. Dry eye may occur when the layers are out of balance and unevenly coat the eye.
The thin, oily (lipid) layer comes from the meibomiam and Zeis glands. These tiny glands line the eyelid’s margin. This outer layer has three jobs:
1. slow the evaporation of the watery middle layer
2. increase surface tension, so tears don’t overflow the lid
3. lubricate the eyelid during blinking
The bulky, watery middle layer comes from the lacrimal gland, which lies beneath a bone near your nose, and the glands of Krause and Wolfring, which are under the eyelids. It works to:
1. supply oxygen to the eye’s surface
2. fight infection with natural antibiotics, such as lactoferrin and lysosomes
3. act as a bulky filling that smoothes the eye’s surface
4. wash away debris, such as dead cells
The inner mucous (mucin) layer comes from goblet cells, Henle’s crypts and glands of Manz. All are found in the clear membrane (conjunctiva) that covers most of the eyeball’s surface and lines the inner eyelids. This thin layer helps tears glide evenly across the eye’s surface. Without it, the other layers of tears would form into tiny droplets instead of a smooth, even coating.
For more information
All about dry eyes. Visual Eyes May 1998. v. 1, no. 2, p. 34
National Eye Institute: http://www.eri.harvard.edu/htmlfiles/dryeye.html