Dry Eyes

By Christine Haran

As the warm humid air of summer lifts and the heat begins to creak on in homes and offices, some people will find that their eyes feel like a sheet of sandpaper. Dry eye syndrome, which can cause dryness, irritation and a gritty sensation, can be exacerbated by dry indoor heating. But there are other tear-stealers, such as wind and soft contact lenses.

This common but frequently undiagnosed syndrome occurs when not enough tears are being produced or when tears are evaporating too quickly. While dry eye can affect anyone, a recent study published in the American Journal of Ophthalmology found that nearly 3.2 million American women over the age of 50 suffer from dry eye syndrome, leading some experts to think it may also be related to hormones. When untreated, dry eye can interfere with daily activities such as driving and reading, and can sometimes impair vision.

Below, Dr. Reza Dana, an associate professor at Harvard Medical School and a researcher at the Schepens Eye Research Institute and Cornea Service at the Massachusetts Eye & Ear Infirmary, discusses how to ease the symptoms of dry eye syndrome.

What is dry eye syndrome?
"Dry eye syndrome" is a name that encapsulates a number of different conditions, all of which share eye dryness. It's like "headache"; there are many different types of headaches and causes of a headache, but they all share the same general symptoms of pain in and around the head region. The different types of dry eye are classified into dryness that has to do with inadequate production of tears, what we call tear-deficient dry eye, and dry eye syndrome that is due to enhanced loss (or evaporation) of the tears. We don't know exactly what percentage of people with dry eye syndrome have each type, and this issue is complicated by the fact that many people have both types of dryness at the same time.

The one thing that all of these patients have in common is a sensation of burning and dryness on their eye, which can be quite debilitating in moderate to severe dry eye.

How common is dry eye syndrome?
It affects far more women as compared to men in all age groups. There are many theories regarding that. But, the overarching hypothesis is that the differences are due to sex hormones.

Male sex hormones, like androgens or testosterone, tend to inhibit many, but not all, forms of immune and inflammatory responses. [Inflammation contributes to dry eye.] And consequently, because women have a much lower amount of circulating testosterone as compared to men, that might be an important factor in predisposing women to dryness. It's theorized that dry eye is more common in women after menopause because there is a decrease in androgens as well as estrogen.

There are now clinical trials ongoing where testosterone drops are actually being given to patients with certain forms of dry eye to see if they respond.

What are the symptoms?
Dryness of the eye can be present without signs or symptoms. But there are several dozen symptoms that can occur, including grittiness, foreign body sensation, irritation, pain, change in vision and redness. These symptoms might be helpful in diagnosis, but on the other hand, they're really not that helpful because there are many other conditions such as allergy, to name one, that can lead to many of the same symptoms. It has taken decades for people to realize that dryness is one of the most reliable symptoms used in the diagnosis of dry eye syndrome.

Are there risk factors for dry eye syndrome?
There are many factors that can either cause or exacerbate dry eye syndrome. A very common cause of dryness in the eye is soft contact lenses. Because soft contacts have a very high water content, they act like a sponge and suck up the moisture on the eye surface.

Another cause of dryness, which we keep seeing more and more of, is LASIK refractive surgery. All the reasons for it are not quite understood. But in essence, the cutting into the cornea leads to a cutting of the nerves whose functioning is important in the physiology of the cornea. And that leads to dryness.

Exposure to dry air, in particular, dry heat, which occurs in people's homes during the winter, or even exposure to air conditioning, which is dry air in the summertime, can also cause dryness. Another factor is exposure to wind.

Medications such as anti-hypertensive medications, diuretics, cardiovascular medications and psychotropic medications, including antidepressants, can lead to significant dryness. Antihistamines used in allergy treatments can also lead to dryness. Also, medications used by older men to control what is called BPH, or benign prostatic hypertrophy, likewise can cause dryness. There are many causes of dryness that can be explained, but there are plenty of people who have dry eye without any identifiable issue.

How does dry eye affect vision?
Two-thirds of refraction, or the bending of light, occurs at the interface between the air and the tear film of the eye. Without this bending, light could not get to the retina (the film in the back of the eye), which is required for vision. When the eye is dry, the tear film on the surface of the eye is not uniformly smooth, so the light does not always get bent in the proper way, and visual distortion occurs. One way of determining if someone has visual distortion from dryness is to have them blink a couple of times. If the distortion goes away, this is a pretty reliable indicator that at least part of their problem is due to dryness.

What does diagnostic evaluation involve?
In general, we assess the patient's symptoms. We do a history evaluation to try to identify contributing factors such as contact lens wear, environmental conditions and medications. Then we evaluate the eye. We use specific dyes called vital dyes, which are put on the eye surface to look at the so-called staining of the eye surface to assess the degree of ocular surface damage, which can be brought on my dryness. The tears carry many growth factors for the eye surface cells so in addition to dryness, lack of tears almost "chokes" many of these cells. We also do a measurement of tear secretion called the Schirmer test.

How is dry eye treated?
The common denominator of dryness is an unstable or inadequate tear film. That can be caused by either deficient tear secretion and/or enhanced evaporation. But in either case, artificial tears can theoretically help.

In general, we recommend using artificial tears without preservatives, as preservatives can irritate the eye. It may be better to buy single-vial doses with a twist-off cap. For people who need the occasional application of artificial tears, the ones in bottles are fine.

Another treatment is the use of punctal plugs. They are commonly used to suppress the drainage of tears by blocking off the outflow drainage system of the eye so that tears stay in the eye longer. There are also anti-inflammatory drops, which work particularly well in the tear-deficient form of dry eye syndrome. There are also many new technologies in the pipeline of biotechnology and pharmaceutical firms designed to address the various facets of dry eye syndrome.

Some people with severe tear-deficient dry eye may have the autoimmune disease called Sjögren's syndrome. These patients have severe dry eye as well as severe dry mouth and are treated with medications that are used to promote the secretion of salivary glands in the mouth, as well as the glands that secrete tears. Some of those medications are being looked into for people with dry eye syndrome.

How do you treat people whose tears evaporate too quickly?
People with evaporative dry eye have a problem with the oil-secreting glands of their eye. The tear film itself is comprised of multiple layers. The most superficial layer, the one that is in contact with the air, is the oil layer. Just like oil layers over vinegar or water, oil also layers over the water layer in the tear film. If you don't have oil covering the water, the water will evaporate much more quickly.

There are a number of treatments that we use to make the openings of these oil-secreting glands function better. These include antibiotics and anti-inflammatory drops.

What advice do you have for people hoping to minimize the effects of dry eye syndrome?
People can minimize exposure to adverse environmental conditions such as wind and dry air, and they can promote a more humid environment by using a humidifier indoors. They can also pay attention to medications that dry the eyes. That doesn't mean that one stops their antidepressant or antihistamine, but someone could potentially use a different type of medication or moderate its use. Other than that, we really don't know how to prevent dry eye syndrome.

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