Screening for ectasia risk: what are we screening for and how should we screen for it?

ow should we screen our patients for postoperative ectasia risk prior to excimer laser corneal refractive surgery, or laser vision correction, in 2013? This has been debated in the literature1-4 and remains a “hot topic” at most meeting venues. The challenge we face as refractive surgeons in daily practice is to most accurately identify individuals who have increased susceptibility for developing biomechanical failure (progressive ectasia), without excluding candidates who may safely benefi t from laser vision correction procedures. In screening, sensitivity (the ability to detect disease) and specifi city (the ability to confi rm absence of disease) are the most basic aspects to evaluate the effi cacy of diagnostic tests. In studies that aim to evaluate screening ability of a test, it is critical to use the appropriate study populations; this may include individuals who have developed a specifi c complication (ectasia after LASIK) or patients who are at known high risk to develop the complication. The fi rst population is easy to identify but diffi cult to fi nd when studying rare complications; the second population is diffi cult to fi nd because, by defi nition, suboptimal strategies for identifying those individuals exist. A reasonable substitute for the “at-risk” group is a population with subclinical or very mild disease, because these are closest to the individuals we want to identify. Patients with disease that is easily identifi ed by other testing are only helpful to establish a basic “proof of concept” that a new test might be able to identify the target population. Among eyes known to be susceptible for ectasia progression are those with relatively normal corneal topography from patients with clinical keratoconus detected in their fellow eyes. Such cases have been designated as “forme fruste keratoconus” (FFKC) by Klyce5 and others. Other reasonable alternatives are cases with progressive ectasia after laser vision correction with no identifi able agreed-upon risk factors.6 The role of Placido-disk based corneal topography and central corneal thickness in screening have been well recognized,7 but shortcomings exist, necessitating that we move beyond, but not discount, the data topography provide as an isolated screening evaluation. A variety of Placido and tomography units and automated screening systems are available and have been proposed to facilitate this screening.8-11 Yet, peer reviewed data, which should provide the critical basis for these technology comparisons, have lagged behind anecdotal information and suppositions. So, what should we do to appropriately screen our patients? Should the primary testing modality be topography, tomography, some combination, or something else? Two articles in this issue of the Journal of Refractive Surgery highlight some benefi ts and possible shortcomings of each approach, when viewed within the context of what is and is not currently known.