Standardized Color-coded Maps for Corneal Topography

Purpose: Modern videokeratoscopy is useful in assessing corneal shape. The purpose of this study is to compare color-coded topographic maps using standardized scales with 1.0- and 1.5-diopter (D) intervals. The authors assessed the use of the two scales for detecting clinically relevant features of corneal topography such as regular astigmatism, irregular astigmatism, early keratoconus, and contact lens-induced corneal warpage. Methods: A total of 50 normal corneas, 50 corneas with contact lenses, 50 that had keratoconus (25 early to moderate and 25 advanced), 50 that had penetrating keratoplasty, 20 that had extracapsular cataract surgery, 17 that had excimer laser photorefractive keratectomy for myopia, 10 that had radial keratotomy, 3 that had aphakic epikeratophakia, and 2 that had myopic epikeratophakia were analyzed with a corneal topographic analysis system. Color-coded maps with 1.0-D intervals (Maguire/ Waring scale) and 1.5-D intervals (Klyce/Wilson scale) were compared. Results: There were no topographic characteristics that were not appreciated with either scale for corneas with dioptric powers that fell within their ranges. Conversely, for corneas that had powers outside the range of the 1.0-diopter scale, but within the range of the 1.5-diopter scale, the former produced a map in which the flattest or steepest areas were artifactually smoothed. Conclusions: This study suggests that the Klyce/Wilson scale (constant, 1.5-D intervals) provides the best combination of sensitivity for detection of clinically significant topographic features and the widest range of coverage of powers that are found on a variety of normal, pathologic, and surgically altered corneas. The adoption of the Klyce/ Wilson scale by all manufacturers of corneal topographic instruments as a primary standard will facilitate communication and will make the interpretation of corneal topography easier for both the expert and the novice.