Ocular surface disease (dry eye) has many causes, all of which in one way or another disrupt the tear film. The tear film is the coating of tears on the surface of the eye that keeps it nourished, lubricated and protected from debris and infection. It also keeps the surface of the eye smooth to help the cornea focus light properly on the retina for clear vision.
The tear film has three distinct layers:
The delicate balance of a healthy tear film can be disrupted in a multitude of ways that lead to ocular surface disease (dry eye), which is broadly categorized into two main types: aqueous-deficient and evaporative.