IATROGENIC KERATECTASIA

The cornea is under constant stress from normal intraocular pressure pushing outward. Collagen bands of the cornea provide its form and biomechanical strength. LASIK thins the cornea and severs collagen bands, permanently weakening the cornea. This results in forward bulging of the posterior cornea, which may progress to a condition known as keratectasia, characterized by loss of best corrected vision and possible corneal failure requiring corneal transplant.

The FDA, laser manufacturers, and refractive surgeons are aware of limits on flap thickness, ablation depth, and diameter of the optical zone imposed by corneal biomechanics. When the FDA initially approved lasers for LASIK, it established a minimum of 250 microns of corneal tissue under the flap after LASIK surgery to prevent corneal instability and progressive forward bulging. Subsequent reports in medical literature indicate that 250 microns is not sufficient to ensure corneal biomechanical stability.20,21 In response, some surgeons stopped performing LASIK or raised the residual stromal thickness limit in their practices. However, the majority of surgeons continue to observe the 250 micron rule initially established by the FDA, even though this limit has been shown to be insufficient.

The 250 micron rule is often violated inadvertently during surgery, as microkeratomes that cut the LASIK flap are unpredictable and produce flaps of varying thickness.22 For this reason, flap thickness should be measured intraoperatively. Most surgeons have not incorporated this important measurement into the surgical procedure prior to ablation, which places patients with thicker-than-expected flaps at greater risk.

Keratectasia may develop months or years following seemingly successful LASIK.23 Since most cases are never reported, the true rate of this devastating complication may never be known. The only way to prevent surgically induced keratectasia is to abandon LASIK altogether. It is important to remember that LASIK is elective surgery. There is no sound medical reason to place patients at risk of vision loss from unnecessary surgery.