Dry eye post-LASIK is a very complex entity. Tears are complex, consisting of three layers: At the bottom is a mucin layer, which helps tears adhere to the cornea. At top is an oily layer that helps prevent evaporation. In between is an aqueous layer, the actual watery component of tears.

Meibomian glands line the inner surface of the upper lid, and secrete the oily layer. If these glands don't exist, then some part of the tear film may not be "protected" against evaporate, inducing quicker tear break up times.

In the image below, the top lid shows a normal, banded pattern of meibomian gland distribution. The lower lid shows atrophy of the glands.

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