Dry eye is a chronic condition in which there is an insufficient quantity or unhealthy quality of tears to lubricate and nourish the eye. Dry eye often goes undiagnosed and untreated, despite being a very common and treatable disease. As the population ages, its prevalence is also increasing. Currently between 20 and 25 million Americans suffer from dry eyes. Women are more prone to suffer from dry eye disease. This includes 3.2 million women over the age of 50 and 15% of all Americans over age 65.
With each blink of the eyelids, tears are spread across the front surface of the eye. Tears provide lubrication, reduce the risk of eye infection, wash away foreign matter on the eye, and keep the surface of the eyes smooth and clear. Tears are necessary to maintain the health of the ocular surface and to provide clear vision. People with dry eyes either do not produce enough tears or have a poor quality of tears. Treatments are directed at improving the tear film balance to maintain good quality vision and minimize symptoms.
What is the Tear Film?
When you blink, a film of tears spreads over the eye, making the surface of the eye smooth and clear. Without this tear film, good vision is not possible. The tear film consists of three layers, each with its own purpose:
- An Oily Layer
- A Watery Layer
- A Mucus Layer
The oily layer, produced by the Meibomian glands in the eyelids, forms the outermost surface of the tear film. Its main purpose is to smooth the tear surface and reduce evaporation of tears.
The middle watery layer makes up most of what we ordinarily think of as tears. This layer, produced by the lacrimal glands in the eyelids, cleanses the eye and washes away foreign particles or irritants.
The inner layer consists of mucus produced by the conjunctiva. Mucus allows the watery layer to spread evenly over the surface of the eye and helps the eye remain moist. Without mucus, tears would not stick to the eye.