Causes of Dry Eye

Causes of Dry Eye

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 outermost layer is the lipid layer. It consists of oil produced by the meibomian glands in the eyelids and helps to keep the eye lubricated and protected by preventing tears from evaporating too quickly.
  • The middle layer is the more watery aqueous layer, which is produced by the lacrimal glands in the upper eyelid. It also helps to keep the surface of the eye lubricated and protected in addition to providing it with nutrients.
  • The innermost layer is the mucin layer, which is produced by cells on the eye’s surface and serves to hold the other two layers of the tear film in place.

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.

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