The tear film that coats the front of the eye is very complex and contains three important layers. The outer layer of the tear film is oily, produced by special glands (meibomian glands) within the eyelid, and this serves to prevent evaporation of the salt water middle layer. Meibomian gland dysfunction occurs when these oil glands are not producing oil or the oil is to thick to release, therefore causing dry eye disease. The salt water middle layer comes from the aqueous gland which is located in the upper, lateral part of your eyelid. Sjogren's is the most common cause of a problem with this layer. The inner layer is made of mucus secreted from cells onto the front surface of the eye and is important in helping the salt water layer spread evenly across the front of the eye.
Blinking spreads the tears across the front of the eye while also causing excess tears to be pushed out of a drainage system that leads from the inner corner of the eyelids into the nose. This drainage system starts at the puncta, which are two small holes in the upper and lower eyelids by the nose, runs through the nasolacrimal duct, and then drains into your nose. This is why your nose starts to run when your eyes are watering.
Dry eye disease is a condition that has many causes, and they are different for everyone. You may be able to pinpoint your one cause, while someone else suffers from dry eyes due to multiple variables. The commonality between most of these dry eye causes is inflammation. Almost all disease is caused from inflammation, and the causes listed below usually result in inflammation.
Without further adieu, here are the 17 most common dry eye cause.