Corneal Swelling (Edema)
 

Corneal edema, or swelling, occurs when there is an inadequate supply of oxygen reaching the cornea due to contact lens wear. Essentially, the cornea becomes smothered by the lens. Sleeping in contact lenses, as with extended wear lenses, greatly increases the risk of corneal edema. In this situation, even less oxygen reaches the cornea because the eyelid is closed over it. Also, the normal blinking of the eye is not present, which helps tears and oxygen to circulate under the lens.

Symptoms of corneal edema included blurred or foggy vision, seeing rainbows around lights, redness, and possibly irritation or pain. Complications of corneal edema include corneal abrasion, a tight lens syndrome (see above), and corneal ulcer or infection. Generally, a lens should not be worn if symptoms of corneal edema are occurring.