Tears are an important element in maintaining healthy eyes. They provide lubrication, reduce the risk of eye infection, wash away foreign matter, and keep the surface of the eyes smooth and clear. Tears maintain the health of the front surface of the eye and allow for clear vision. When you blink, tears are spread across the eyes. Dry eye is a condition in which the eyes either do not produce a sufficient amount of tears or produce poor quality tears and fail to properly lubricate and nourish the eyes. Dry eye syndrome is a common and often chronic problem more commonly seen with older age, especially in women, because you produce fewer tears with age.
Symptoms of dry eye include irritated, gritty, scratchy, or burning eyes, a feeling of something in the eyes, excess watering, and/or blurred vision. If dry eye syndrome is not treated it can lead to damage to the front surface of the eye and impair vision. Treatment of dry eye aims to restore or maintain a normal amount of tears.
Evaporative Dry Eye: Evaporative dry eye is commonly associated with deficiency of the lipid layer of the tear film (which exists to protect the tears from evaporating too rapidly). This can be the result of lid infections, lid gland dysfunction or related conditions. When the lipid layer is poor, the tear film becomes particularly vulnerable to other adverse conditions such as climactic factors, wind, heating/air conditioning, etc. The term evaporative dry eye is sometimes used too broadly for all dry eye conditions excluding aqueous deficiency.
Aqueous Deficiency: Tears are made up many substances secreted from various parts of the lacrimal system. The conditions collectively referred to as “dry eye” can occur for many reasons, the most obvious reason being insufficient quantity of tears. An aqueous deficiency refers specifically to inadequate production by the lacrimal glands or the watery part of the tears. Aqueous deficiency is what really properly ought to be called “dry eye” – when you’re aqueous deficient, you really are dry. This is contrasted with Evaporative Dry Eye where the primary problem is – or at least starts out as – poor production or secretion of the oil layer. However, the lines become blurred as the diseases progress. Aqueous deficiency is most frequently associated with autoimmune diseases (most notably Sjögrens Syndrome). Other well known causes are LASIK or other laser eye surgeries, where patients experience primary aqueous deficiency at least temporarily, and some permanently, due to severing of the nerves; and side effects of many medical treatments such a radiation or chemotherapy which may cause permanent damage to the lacrimal glands.