The Real Cause and Extent of Evaporative Dry Eye
There are two predominant forms of Dry Eye. Evaporative, due to lipid deficiency, is the most prevalent, affecting 65% to 86% of sufferers with dry eye symptoms1,2.
Evaporative Dry Eye occurs when the aqueous evaporates at a faster rate than normal due to an inadequate protective lipid (oil) layer on the surface of the tear film. This is a manifestation of reduced lipid excretion from the oil-producing meibomian glands found within the eyelids. Aqueous Deficient Dry Eye occurs when tear aqueous generation from the lacrimal gland is insufficient to keep the eyes moist.
The two forms have been difficult to distinguish, since tools to assist physicians in differentiating dry eye etiology have not been available. Instead of determining etiology and initiating effective treatment, many patients have been treated patients based on the level of symptom severity.
Using traditional treatment approaches, there has been little incentive to depart from this course and identify the lipid deficient etiology.
Recognizing the symptoms of Evaporative Dry Eye
A leading, but commonly overlooked, cause of dry eye is meibomian gland dysfunction due to internal obstruction. It is usually not accompanied by obvious inflammation or other signs.
Physicians often suspect dry eye based on frequently reported symptoms, including dryness, discomfort and irritation, tiredness, sensitivity to light and grittiness. This is especially true in the presence of other symptoms such as pain or foreign body sensation, ocular fatigue, tearing or mucus discharge, transient blurring, symptoms that worsen later in the day, and contact lens intolerance.
The perspective of patients impacted by moderate-to-severe symptoms of dry eye differs from that of their physicians. For sufferers it is a high-involvement, lifestyle-impairing chronic disease with marginal or inadequate treatment.
1 Shimazaki J, Sakata M, Tsuboto K. Ocular Surface Changes and Discomfort in Patients With Meibomian Gland Dysfunction. Arch Ophthalmol. 1995;113(10):1266 1270.
2Lemp MA, Crews LA, Bron AJ, Foulks GN, Sullivan BD. Distribution of aqueous deficient and evaporative dry eye in a clinic-based patient population. Cornea. In press.