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San Francisco-Topography detects the early curvature changeson the anterior corneal surface. And these are precisely thechanges that need to be heeded in patients undergoing refractivesurgery. These changes may have been ignored previously andresulted in the development of vision-threatening ectasia, reportedStephen D. Klyce, PhD, who spoke at the annual meeting of theAmerican Society of Cataract and Refractive Surgery.
To underscore the potential importance of the early curvatures changes, Dr. Klyce recounted a case in which a patient had mild corneal curvature changes before LASIK. The visual outcome was good for 3 months after the surgery. After 18 months, however, the patient developed keratectasia and ultimately required bilateral corneal transplants.
"With progression, thinning of the cornea can be detected with pachymetry and a diagnosis made," he said.
Corneal ectasia stages
There are two stages associated with corneal ectatic diseases, Dr. Klyce said. The first is the suspect stage (forme fruste keratoconus, suspect pellucid marginal degeneration) in which the usual sign with just Placido disc corneal topography is abnormal steepening in an area of the cornea; in some cases there may be changes on retinoscopy. In the second stage, in which diagnosis is possible, Dr. Klyce explained, along with the aforementioned abnormalities, the clinician can see changes in pachymetry and changes that are visible during the slit lamp examination.
He also described a fortituous case in which the patient did not undergo refractive surgery. This patient had wanted to undergo LASIK and initially had mild inferior steepening. She had had suspected keratoconus and had had a 7-year progression to clinical keratoconus. Ten years later, her corneas are stable with functional spectacle-corrected vision in the worse eye of 20/40 and 20/25 vision in the fellow eye. If she had undergone LASIK when she presented to the refractive practice, the status of her eyes would be highly questionable now, Dr. Klyce emphasized.
Ophthalmologists should use caution when faced with these patients, Dr. Klyce advised.
"There are indexes that are available, such as that of Yaron Rabinowitz, MD [Los Angeles], and Peter J. McDonnell, MD [Baltimore], who were the first to develop an index to draw a line between normal corneal variations and corneas that can be considered to have suspected keratoconus," Dr. Klyce said. "Since that time we have other more sophisticated means to make this differentiation.
"We must be careful," Dr. Klyce concluded. "We are learning to lower the bar to see these patients who have abnormal inferior steepening in order to avoid the later vision-threatening consequences in susceptible patients."