The cornea, or clear outer surface of the eye, is normally round and smooth, which allows sharp focusing of light onto the retina and clear vision. In keratoconus, the cornea becomes progressively thinner and more pointed. This pointing of the cornea causes distortion of vision that usually cannot be corrected with glasses. Hard contact lenses can be used to provide a more normal, rounded shape to the surface of the eye, but when the disease becomes advanced, contact lenses will not fit properly and a corneal transplant is necessary to restore vision.

DALK or deep anterior lamellar keratoplasty is a partial thickness corneal transplant procedure that removes the portion of the cornea that is thinned and diseased, but retains the normal endothelial layer, or innermost layer of the cornea. As a result, the DALK procedure has less risk of rejection and is the preferred procedure in cases of keratoconus.