The term dry eye encompasses a constellation of signs and symptoms. Dry eye (Ocular Surface Disease) has traditionally been believed to be primarily due to a lack of watery tears produced by the lacrimal gland above the eye. More recently, the complexity of the tear film and ocular surface has become increasingly apparent.
Dry eye can be categorized into two distinct groups:
• Aqueous deficiency dry eye
• Evaporative dry eye
Most cases of dry eye are now believed to be primarily evaporative in nature – either due to meibomian gland dysfunction (lipid producing glands in the lids) or lipid insufficiency. Tear evaporation also contributes to many cases of aqueous deficiency dry eye. Any imbalance can lead to a down spiral of dysfunction.
Because the tears are so complex and structured, all tear components need to be in balance. Part of the balance and function is neurological control. Sensory inputs to the brain create a complex feedback loop that controls the production of all tear components and functions. Damage caused by infection (such as herpes infection of the eye) or surgery (such as LASIK) can lead to dry eye, in some cases severe.
As dry eye worsens, inflammation becomes a greater part of the disease profile. While many cases of dry eye are relatively mild, some may progress to cause severe damage to the ocular surface and loss of vision.
Symptoms of dry eye include:
• Unstable or blurry vision
• Environmental sensitivity (increased symptoms on airplanes or cars)
• Burning or stinging of the eyes
• Tired or fatigued eyes
• A gritty sensation
• Irritation or pain
• Contact lens intolerance or reduced wearing time
• Reduced reading or near working time