dry eye
Dry Eye: A Look at the Numbers
With the prevalence of dry eye sufferers in the United States, it only makes sense to know more about the condition.
BY MILTON M. HOM, O.D., F.A.A.O., AND PETER A. SIMMONS, PH.D., F.A.A.O., Azusa, Calif. and Irvine, Calif.

How many people have dry eyes? The numbers are hardly definitive. Estimates vary from four million in the United States to almost 60 million worldwide. And even though we only have estimates, we do know that many people suffer from varying degrees of dry eye. Here's what the experts say about this condition.

ILLUSTRATION BY DEAN PROUDFOOT

A word from the experts

Public health experts distinguish between people presenting themselves to their practitioners and the actual prevalence of dry eye in the entire population. We may expect higher numbers in the general population because many people don't seek professional care. Thus, some studies focus on numbers seen by medical professionals and others focus on patient populations themselves.

A recent study by Schaumberg, et al., (American Journal of Ophthalmology 2003;136(2), 318-326) of the epidemiology of dry eye syndrome in a large group of U.S. women indicates that nearly 7% of women aged 50 years and older experience severe symptoms of dry eye disease or have been diagnosed with dry eye. This translates to a total of about three million women in this age group. We can add at least one million men in the same age group to this total, plus additional patients who fall within younger age groups.

The criteria determining dryness has a strong effect on the numbers. In the study just mentioned, the three million women accounted for those needing therapeutic intervention for ocular dryness. The patients classified as having dry eyes fell within the moderate and severe categories. Some experts feel that this number is too low because most dry eye patients fall into the mild category. In addition, these figures were projected from 1999 census data, so current values are likely higher.

Reviewing study results

From an eyecare practitioner's point of view, dry eye may be one of the most commonly reported conditions. Just consider the fact that more than half of all laser-assisted in situ keratomileusis (LASIK) patients have symptoms following surgery (Hovanesian, et al., Journal of Cataract and Refractive Surgery 2001: 27(4), pp 577-584). With such a high incidence, dry eye evaluation and intervention before LASIK is becoming a standard of care.

For general optometric practice, the best recent data comes from a University of Waterloo survey of Canadian practices. The survey revealed that almost 30% of patients experienced some level of symptoms of dry eye, with a significantly higher proportion of dry eye symptoms among contact lens patients, women and in individuals aged 70 years or more.

In another survey, 64% of non contact lens wearers and 80% of contact lens wearers reported ocular discomfort at least infrequently. Only about 20% of non lens wearers reported dryness, compared to between 70% and 80% of lens wearers. In this same study, investigators diagnosed dry eye in 22% of non contact lens wearers and 15% of contact lens wearers, illustrating the commonly observed difference between patient reports of discomfort and actual disease. Irrespective of what public health experts believe, symptoms of dryness are ubiquitous to the eyecare practitioner.

Add them up

Another way to determine the number of dry eye patients is to count the number of dry eye products sold. The number of patients may be estimated from the unit sales of artificial tear products. Industry data indicate that U.S. consumers purchased approximately 30 million units of artificial tear products in 2002. In addition to artificial tears, consumers (some of whom may have been dry eye patients) bought about 25 million units of red eye products.

Assuming that patients purchase between five and 10 units of dry eye products each year, this gives an estimate of three million to six million patients in the United States, or slightly higher if we include red eye products in the estimate. This accounts for approximately 2% of the total U.S. population. Many make the argument that three to six million is still a low figure. As we all know, significant numbers of people don't seek professional treatment or treat themselves with over-the-counter remedies.

The range of effectiveness for each type of drop is indicated by the shading of its bar. Mild dryness benefits from low viscosity tears. We can treat moderate severity with mid-viscosity drops. Cyclosporine (Restasis) in its emulsion vehicle should have a broad range of effectiveness. The top three bars indicate over the counter products.

Why do the numbers vary?

Dry eye takes on many forms: Two patients who have the same condition can have a variety of histories and chief complaints. For the sake of simplicity, we can divide the causes of dry eye into internal and external.

Internal causes. These include systemic diseases or other autoimmune diseases that affect the lacrimal glands, congenital problems with the lacrimal apparatus, corneal surface disease leading to tear film disruption, and any of a number of problems with the lids or the blinking mechanism. Decreased levels of circulating androgens in older women have also been linked to dry eye disease.

External causes. These include side effects of systemic or ocular medications, contact lens wear, ocular surgery (particularly LASIK), seasonal allergy and environmental factors such as dry, windy conditions; excessive air conditioning; etc. Environmental factors are often the wild card.

It's in the air

Even the slightest environmental change can alter the patient's dry eye comfort state. Often a change of medication, solution or avoidance of specific environmental triggers can make all the difference in a patient's ability to cope with his dry eye condition.

Draw a distinction

A recent study of more than 1,500 patients showed a 10.8% overall prevalence of dry eye. The researchers divided the group into the following dry eye subtype categories: lipid anomaly dry eye (LADE), aqueous tear deficiency (ATD), primary mucin anomalies, allergic/toxic dry eye (ADE), primary epitheliopathies and lid surfacing/blinking anomalies (LSADE).

LADE was the most prevalent subtype, occurring in 4.0% of all patients in the sample (see "Subtypes of Dry Eye Disease"). Unfortunately, no test reliably distinguishes between these in clinical practice and many patients may have several problems leading to their dry eye complaints.

However, this finding is interesting because it suggests that 70% of dry eye cases are caused by either meibomian gland dysfunction or are related to allergy. This means that you should pay particularly careful attention to these possibilities when examining a dry eye patient.

Treat according to severity

The easiest approach to diagnosing dry eyes from a clinical perspective may be severity. The most commonly accepted grading system among dry eye experts is classifying the condition as mild, moderate or severe. Once you establish severity you can then appropriately design a treatment regimen.

Low viscosity tears or drops work well for mild dryness and may be suitable for use with contact lenses. Thicker (mid-viscosity) eye drops and gels work well for patients who experience moderate dryness.

Patients who have evaporative dry eye, meibomian gland dysfunction and more severe symptoms are probably candidates for a new emulsion drop designed to enhance the lipid layer of the tears. The additional benefit of this emulsion drop is the minimal effect on vision combined with superior residence times. When dry eye symptoms, regardless of severity, are chronic in nature, underlying inflammation is likely, indicating anti-inflammatory treatment.

Treating chronic dry eye

Previously, suppression of inflammation in dry eye was only possible with steroids or with custom compounded cyclosporine (if available). Now the Food and Drug Administration has approved cyclosporine in a vehicle containing castor oil, glycerin and other ingredients as the first true pharmaceutical treatment for dry eye. The approved indication is to increase tear production in patients who have keratoconjunctivitis sicca because of ocular inflammation. What proportion of dry eye patients will be candidates for this treatment option has yet to be determined, but clearly practitioners will prescribe it for any patient who has chronic disease and/or who hasn't achieved relief from conventional treatments.

As one possibility, cyclosporine may become a non-surgical alternative to punctal occlusion, particularly for those patients who have frank aqueous deficiency (e.g. low Schirmer). Since the approved formulation of cyclosporine also provides lipid layer enhancement, it may provide some benefit in preventing the progression of dry eye disease by both reducing inflammation and stabilizing the tear film. The chart on page 64 shows a suggested treatment algorithm considering all of these options.

Talk to your patients

The numbers indicate that at least three million dry eye patients in the United States need professional intervention for diagnosis and treatment. A larger number, perhaps 30% of all patients in O.D.s' offices, have some experience of dry eye. The proportion increases to at least 50% for contact lens wearers and perhaps even more in post-LASIK patients. From these numbers we should consider dry eye a standard issue to review with all patients so we can care properly for this common problem.

References available on request.

Dr. Simmons conducts research and development projects within the Consumer Eye Care Group at Allergan, Inc., with particular interests in the area of dry eye disease and treatment.

Dr. Hom just finished compiling Ocular Drug Consult, which Elsevier Science will publish in early 2004.