Considerable progress has been made in recent years in the understanding of the epidemiology of dry eye disease. Here, two doctors discuss some of the studies that have helped ophthalmologists understand the prevalence, burden, and risk factors of dry eye disease. They also highlight how improved diagnosis will have a significant effect on the quality of life of patients with dry eye.
Epidemiologic studies show wide differences in prevalence. Estimating the prevalence of dry eye disease is problematic because consensus on diagnostic criteria does not exist. Another reason for the variation in prevalence estimates may be a true heterogeneity in dry eye prevalence in different populations.
A review of several large studies, conducted by the Epidemiology Subcommittee of the 2007 DEWS, showed that the prevalence of dry eye ranges between 5% and 30% in people aged more than 50 years.1 Considering the different definitions used in those studies, the DEWS group concluded that the true prevalence of moderate to severe dry eye lies somewhere close to the lower end of the range, whereas inclusion of mild or episodic cases would bring the estimate closer to the higher estimates reported.
A further difficulty in establishing the extent of dry eye disease is the fact that it is an underdiagnosed condition. Many patients mistakenly attribute dry eye symptoms to other causes such as aging and assume the symptoms are simply something they have to live with. As a result, many patients tend to endure the condition or to self-treat with over-the-counter products without consulting a physician or obtaining a definitive diagnosis. Indeed, the results of the 2005 Gallup Survey of Dry Eye Sufferers suggest that one in four people with dry eye do not consult a health-care professional about their condition.2
Who is at risk?
It is commonly accepted that the prevalence of dry eye disease increases with age and is greater in women, especially after menopause.1
Sex hormones are recognized as playing an important role in ocular surface homeostasis, and studies are investigating the mechanism(s) by which disturbances may result in dry eye. Androgens decline with aging in both men and women, and androgen deficiency has been shown to increase the risk of dry eye in several clinical situations, such as Sjögren's syndrome, premature ovarian failure, and anti-androgen therapy.1
Two large epidemiologic studies conducted in the United States have provided further insight into the relationship between sex hormones and dry eye: the Women's Health Study (WHS) in nearly 40,000 female health professionals, and the Physicians' Health Study (PHS) in approximately 22,000 older male physicians. Results showed that the prevalence of severe to moderate dry eye increases from approximately 5.7% in pre-menopausal women (aged fewer than 50 years) to 9.8% in women aged more than 75 years.3 Dry eye disease also was shown to be about 50% more common in women than in men, with an estimated 3.23 million women and 1.68 million men aged more than 50 years having moderate to severe dry eye.4
Moreover, post-menopausal hormone therapy appeared to increase dry eye prevalence in women. Compared with women taking no hormones, those taking only estrogen had a 72% higher risk of having dry eye, whereas those taking estrogen with progestin had a 26% higher risk.