Ten caveats in keratorefractive surgery.

Topographic shifts in the cornea are associated with refractive changes as follows: (1) The normal cornea flattens over any incision. (2) Radial incisions flatten the adjacent cornea and the cornea 90 degrees away. (3) The cornea flattening effect increases as incisions approach the visual axis. (4) The cornea flattens directly over any sutured incision. (5) The cornea flattens adjacent to loose sutures and flattens 180 degrees away, and steepens 90 degrees away. (6) The cornea steepens adjacent to tight sutures and steepens 180 degrees away, and flattens 90 degrees away. (7) The cornea flattens over wedge resection or tucks. (8) The cornea steepens anterior to wedge resections or tucks. (9) Tissue removal produces corneal flattening over the site of tissue removal, whether traumatic or surgically induced. (10) Full-thickness corneal tissue addition produces corneal steepening over the site of the tissue addition and flattens the adjacent cornea.