1. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group The impact of reference body selection for calculating Posterior Corneal Elevation for Diagnosing Keratoconus: BFS x BFTE Ana Laura C. Canedo, MD Purpose: To compare the sensitivity and specificity for diagnosing keratoconus using elevation maps calculated from the floated Best Fit Sphere (BFS) and Best Fit Toric Ellipsoid (BFTE) for the 8mm area. e-Poster Ambrósio et al. Renato Ambrósio Jr, MD, PhD; Ricardo Lousada, MD; Marcella Salomão, MD; Bruno Valbon, MD; Frederico P. Guerra, MD; Michael W. Belin, MD, FACS

2. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group e-Poster Retrospective observational case-control study 98 normal corneas from 49 patients and 56 keratoconic corneas from 28 patients Pentacam HR rotating Scheimpflug camera (Oculus, Wetzlar, Germany). Diagnosis of keratoconus or normal was based on a comprehensive ophthalmological examination, including corneal topography (Placido) and Ocular Response Analyzer (ORA, Reichert, New York) biomechanical analysis. Anterior (f-front) and Posterior (b-back) corneal elevation maps were calculated using two different reference surfaces that best fit to the 8mm corneal area: best fit sphere (BFS) and best fit toric ellipsoid (BFTE). The following measurements were obtained: Apex: A “true” thinnest: TT (from the Pentacam software) “displayed value closest to” thinnest”:TC (from JPEG image) “true” more elevated within 4mm: TME (from the Pentacam software) “displayed value closest to” more elevated within 4mm ”: ME (from JPEG image) Receiver operating characteristic (ROC) curves were used to determine the test’s overall predictive accuracy (area under the curve) and to identify optimal cutoff points to maximize sensitivity and specificity in discriminating keratoconus from normals. Mann-Whitney test was used for assessing whether each variable had the same distribution in normals and keratoconic corneas. Methods

3. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group BFS – Best Fit Sphere for Front and Back Elevation TME TME – True More Elevated within 4mm ; ME - More Elevation Closest from JPEG TC – Thinnest Closest from JPEG ; TT – True Thinnest A -- Apex +44 ME TC +22 +42 APEX

4. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group BFTE – Best Fit Toric Ellipsoid TME ME +18 TME +43 ME TME – True More Elevated within 4mm ; ME - More Elevation Closest from JPEG TC – Thinnest Closest from JPEG ; TT – True Thinnest RF – r flat RS – r steep APEX TT RFRS

5. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Results There was a statistical significant difference for all elevation values from normal and keratoconus, considering anterior and posterior corneal data, referencing to BFS and BFTE (Mann-Whitney Test, p<0.05). Best cut off for the posterior elevation at the thinnest and apex for BFS were 21 and 9 microns, with respective AUROC of 0.98 and 0.87. Best cut off for the posterior elevation at the thinnest and apex for BFTE were 13 and 6 microns, with AUROC of 0.97 and 0.86 respectively SensitivitySpecificityCriterionAUROC Standard Error BFS b TME 100 >2310 BFS b TT 100 >1910 BFS b TC 10096,9>170,9990,0007 BFTE b TT 10098120,9990,000911 BFS f TC 10095,9>50,9980,00138 BFTE b TC 94,6100>160,9980,00166 BFS f TT 96,499>60,9970,00218 BFTE b ME 96,496,9>200,9940,00398 BFTE f TT 92,998>60,9920,00497

6. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Elevation Reference Body Front SensitivitySpecificityCriterionAUC Standard Error BFS f91,184,7<=7.720,9230,0227 r flat f80,486,7<=7.510,8880,029 r steep f82,199<=7.180,9690,0111 ave r-s f96,485,7<=7.540,9530,0161 BFS fr flat fr steep fave r-s f BFS f10,0140,0080,001 r flat f10,0020,01 r steep f10,165 ave r-s f1 P-value for ROC Comparisons

7. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Elevation Reference Body Back SensitivitySpecificityCriterionAUC Standard Error BFS b83,983,7<=6.360,9070,0259 r flat b73,289,8<=6.250,8810,03 r steep b83,995,9<=5.940,9510,0194 ave r-s b83,993,9<=6.150,9420,0191 BFS br flat br steep bave r-s b BFS b10,1640,0240,003 r flat b10,0230,003 r steep b10,502 ave r-s b1 P-value

8. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Corneal Elevation Front: More Elevated within 4mm SensitivitySpecificityCriterionAUC Standard Error BFS f ME 98,284,7>130,9640,0132 BFS f TME 96,4100>140,09870,0106 BFTE f ME 96,490,8>70,960,0222 BFTE f TME 96,499>80,970,0202 BFS f MEBFS f TMEBFTE f MEBFTE f TME BFS f ME10,030,8230,713 BFS f TME10,0560,172 BFTE f ME10,03 BFTE f TME1 P-value

9. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group SensitivitySpecificityCriterionAUC Standard Error BFS b ME 96,492,9>300,9820,00805 BFS b TME 100 >2310 BFTE b ME 96,496,9>200,9940,00398 BFTE b TME 98,299>180,990,00139 BFS b MEBFS b TMEBFTE b ME BFTE b TME BFS b ME10,0250,1390,04 BFS b TME10,1560,294 BFTE b ME10,144 BFTE b TME1 P-value Corneal Elevation Back: More Elevated within 4mm

10. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Corneal Elevation Front: Thinnest SensitivitySpecificityCriterionAUC Standard Error BFS f TC10095,9>50,9980,00138 BFS f TT96,499>60,9970,00218 BFTE f TC92,996,9>50,9830,00985 BFTE f TT92,998>60,9920,00497 BFS f TCBFS f TTBFTE f TCBFTE f TT BFS f TC10,4360,0940,145 BFS f TT10,0870,131 BFTE f TC10,093 BFTE f TT1 P-value

11. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Corneal Elevation Back : Thinnest SensitivitySpecificityCriterionAUC Standard Error BFS b TC10096,9>170,9990,0007 BFS b TT100 >1910 BFTE b TC94,6100>160,9980,00166 BFTE b TT10098120,9990,000911 BFS b TCBFS b TTBFTE b TCBFTE b TT BFS b TC10,4360,0940,145 BFS b TT10,0870,131 BFTE b TC10,093 BFTE b TT1 P-value

12. e-Poster ALC Canedo, MD 2010 Rio de Janeiro CornealTomograhyandBiomechanics Study Group Study Group Discussion and Conclusions All elevation parameters studied had statistically significant differences among keratoconus and normal (Mann Whitney Test). There were statistically significant ROC curves for some parameters, favoring BFS to BFTE to diagnose keratoconus but both BFS and BFTE served as good reference bodies for elevation maps and had excellent performances to discriminate keratoconus from normal corneas. The elevation values at the thinnest point were more consistent and had better ROC curves than the values at the apex. The posterior elevation at thinnest point using BFS provided the best performance in this study with the sensitivity of 96.7% and specificity of 99%. This study did not address very early forms of ectasia, such as sub- clinical keratoconus and forme-fruste keratoconus Future studies to correlate elevation and pachymetric distribution data, along with biomechanical parameters are need to determine Ectasia Susceptibility