KERATOCONUS AND CONTACT LENS-INDUCED CORNEAL WARPAGE ANALYSIS USING THE KERATOMORPHIC DIAGRAM

Purpose. Videokeratography of early keratoconus may be difficult to di stinguish from contact lens-induced corneal warpage, even by experienc ed examiners. Furthermore, topographic irregularity may be judged inco nsistently if quantitative standards are not applied, Quantitative mea sures based on videokeratographic data were developed and evaluated to determine if improved corneal topographic classification can be achie ved. Methods. The Corneal Irregularity Coefficient (CIC) and Corneal P ower Coefficient (CPC) were derived from multiple measures of mean cor neal power and its variance for 207 videokeratographs of normal, warpe d, keratoconus, and keratoconus-suspect corneas, CIC was plotted again st CPC, creating a distribution of points representing all maps that t ended to be grouped according to surface conditions (the Keratomorphic Diagram). Normal, steep, abnormal, and warped zones were defined by C IC and CPC cutoff values chosen to distinguish normal from keratoconus corneas graphically. Results. Seventy of 76 normal corneas were group ed in the normal zone and 6 in the steep zone; 84 of 84 keratoconus co rneas were grouped in the abnormal zone; 35 of 35 contact lens-induced warpage cases were grouped in the warped zone; and 10 of 12 keratocon us-suspect corneas were grouped in the warped zone, with 2 in the abno rmal zone. Serially plotted data of keratoconus progression and warpag e regression demonstrated that the vector displacement of CIC and CPC values may provide a potentially useful means of distinguishing contac t lens-induced warpage from keratoconus-suspect corneas. Conclusion. T he Keratomorphic Diagram aids in classifying and comparing corneal sha pe by plotting indices along axes with easily recalled scales. The dia gram may become a useful tool to assess presurgical corneal surface in stability and postoperative progression of corneal shape change due to healing.