Multiple tests lead to a relatively better, but not absolute, chance of detecting forme fruste keratoconus

François Malecaze

ABU DHABI — Detection of forme fruste keratoconus is a major problem in corneal refractive surgery due to the risk of iatrogenic ectasia.

"The problem lies all in the 'gray zone,' where we might equally incur in false positives and false negatives," François Malecaze, MD, said at the World Ophthalmology Congress here. "In order to establish whether we are dealing with pathological or physiological values, we need to increase specificity and sensitivity of tests. Perform multiple tests, and for each of them, multiply the indexes."

For instance, both reflective and elevation topography should be used. In topography, symmetric vs. asymmetric patterns can help discriminate between congenital astigmatism and early signs of keratoconus. A loss of enantiomorphism is also an early diagnostic finding. Characteristic signs in elevation tomography are the posterior bulge and the location of thinnest point outside the central 4 mm.

Ocular Response Analyzer (Reichert) indexes for corneal biomechanics are theoretically interesting but not always effective in practice. Wavefront analysis has introduced the important parameter of increased coma. Studies on genetic and biochemical methods are under way.

"We must be aware, however, that whatever the technology, it will probably never be possible to detect forme fruste keratoconus with 100% reliability. Multiple arguments and caution are the rule. And when in doubt, do not hesitate to cancel the surgery," Dr. Malecaze said.

Disclosure: Dr. Malecaze has no relevant financial disclosures.