TOPOGRAPHIC PATTERN AND APEX LOCATION OF KERATOCONUS ON ELEVATION TOPOGRAPHY MAPS

Purpose. To compare topography pattern and apex location in elevation and axial curvature topographic maps of keratoconic corneas. Methods. We prospectively evaluated 72 corneas of 42 patients who had one or mo re corneal findings of keratoconus with the elevation and axial curvat ure displays of the PAR Corneal Topography System (PAR-CTS) and 66 of these corneas with the axial curvature display of the Tomey Topographi c Modeling System (TMS-1). Topography maps were evaluated for topograp hy pattern and location of the cone apex. Results. Axial curvature dis plays of the PAR-CTS and the TMS-1 showed good concordance in terms of topographic patterns (96% for right, 86% for left corneas) and apex l ocations of cones (92% for right, 80% for left corneas). On the other hand, low concordances were noted when comparing topographic patterns (35.3% for right, 36.8% for left corneas) and apex locations (47% for right, 38% for left corneas) on curvature and elevation mode displays of PAR-CTS. Apices were found in the inferotemporal quadrant in 65% of corneas evaluated with the PAR-CTS. This distribution is significantl y different from the apex location in axial curvature maps (p < 0.04). Twenty-nine percent of corneas that showed an apex on the axial curva ture mode of the PAR-CTS had a normal pattern, without a detectable co ne apex, on the elevation mode display. Conclusions, The results of th is study clearly show the difference between elevation and curvature-b ased corneal topographic evaluation of keratoconus. Unlike axial curva ture maps, the majority of apices on elevation maps are clustered in t he inferotemporal quadrant. This new information about apex location i n keratoconic corneas provided by elevation topography may have better diagnostic specificity than regional differences of curvature on axia l curvature maps. Because elevation mapping shows the physical locatio n of the cone, it may improve results of contact lens fitting and surg ical management.