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Emilia Cantera, Magdalena Cortes, Silvia Conflitti; Cone Apex In Keratoconus, Evaluation With Two Different Topographic Algorithms. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1110.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:. Corneal topography is used to evaluate the progress of keratoconus. Considered the algorithms variety for mapping cornea, it is important to understand how these maps related. The purpose of the study is to compare the position and the magnitude of the cone apex as a function of topography algoriyhms.
Methods: 50 eyes of 25 keratoconic patients without severe corneal clinical signs have been evaluated .Eyes have been divided in two groups according to the cone apex value (1 group: < 50D - group 2: > 50D) . Videokeratography was performed with a large mire topographer Eye-Map (CSO). Axial and Tangential algorithms were generated from each image and the steepest curvature (cone apex), was manually determined using the cursor. We have compared the cone magnitude (dioptric value), position of the cone apex (meridian), distance of the cone apex from the center of the map between the two algorithms.
Results: Differences between the axial and tangential algorithms were found for magnitude and distance while the meridian was similar and no statistically significant ( Group 1-Axial: mean 272,09±19,39; Tangential:mean 274,36±19,01; Group 2-Axial: mean 268,53±5,45; Tangential:mean 274,36±12,94) . The dioptric power of the apex of the cone, in tangential algorithm, was higher than the axial one in both groups but was statistically significant (p<0,5) only in the group 2 ( Group 1-Axial: mean 45,45±1,11; Tangential:mean 46,29±1,75; Group 2-Axial: mean 49,78±2,91; Tangential:mean 51,91±1,27) .The distance of the apex from the center of the map was shorter in tangential algorithm in both groups. ( Group 1-Axial: mean 1,71±0,53; Tangential:mean 1,36±0,46; Group 2-Axial: mean 1,97±0,71; Tangential:mean 1,66±0,56)
Conclusions: Cone apex evaluation could vary significantly as a function of used topographic algorithm. Differences are important to considered in the topographic evaluation of the keratoconus follow-up.
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