BACKGROUND: Keratomileusis is a procedure that alters the shape of the cornea for the purpose of correcting refractive error. In myopic keratomileusis, the central cornea is flattened by the removal of stromal tissue. Laser in situ keratomileusis is a technique that involves the surgical resection of a specified amount of corneal tissue and the removal of stromal tissue by excimer laser. When the cornea's tensile strength is diminished, the anterior or posterior corneal surface may protrude. Many cases of iatogenic anterior changes in the corneal surface have been reported and studied, however changes in the posterior surface of the cornea are not as well understood. We report two cases of posterior corneal ectasia after Lasik surgery.
CASE REPORT(S). Our two patients, a 51 year old dentist and a 49 year old office manager, were both referred to us for contact lens fittings. They both shared the same visual complaint: longstanding fluctuating vision following bilateral lasik. Anterior topographies and slit lamp examinations revealed irregular astigmatism and clear corneas OU in both cases. Numerous rigid lens fittings were unsuccessful for our patients and did little to improve vision. Slit scanning topography (ORBSCAN) later revealed a bilateral anterior protrusion of the posterior cornea in both patients.
CONCLUSIONS. The anterior corneal complications following lasik procedures have been well studied, however, little is known about the anterior shift of the posterior curve of the cornea. Because rigid gas permeable lenses were unsuccessful in improving vision in our two patients, we concluded that the decrease in vision might be attributed to something other than irregularities of the anterior corneal surface. The ORBSCAN, a pancorneal slit-scanning topography system provides elevation maps of the anterior and posterior surface of the cornea. Using this system, we found a forward shift in the posterior cornea in both of our patients. As demonstrated in our cases information about the anterior as well as the posterior curvature of the cornea was equally important in our assessment and understanding of our patients' visual concerns.