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Arvo 2010 Final

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Presentation given at ARVO 2010 conference.

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Arvo 2010 Final

  1. 1. Does the Posterior Corneal Elevation Provide the First Indication of Keratoconus? K.C. Baker, Y.-L.Chen, L.Shi, J.W. L. Lewis, L.Kugler, M.Wang. Wang Vision Institute, Nashville, TN; Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN; Department of Ophthalmology, University of Tennessee, Memphis, TN Program # 4963 Poster # D759
  2. 2. Purpose : <ul><li>The purpose of this study is to examine optical characteristics of keratoconus (KC) and forme fruste keratoconus (FFKC), and investigate whether an irregular shaped posterior cornea is a better indicator than the anterior surface that is often used in KC screening. </li></ul>Subject Makeup <ul><li>18 KC and 22 astigmatic eyes were used during this study. </li></ul><ul><li>KC eyes comprise of 8 mild ( BCVA of 20/25 or better ), 5 moderate ( BCVA between 20/30-20/40 ), and 5 advanced ( BCVA worse than 20/40 ). </li></ul><ul><li>FFKC (i.e. mild KC) diagnosis relied on the other eye's condition from the same subject, other KC indications , and family history . </li></ul><ul><li>Astigmatic eyes all had a BCVA of 20/25 or better . </li></ul>
  3. 3. Methods : <ul><li>Analyze anterior and posterior elevation using Pentacam system to evaluate their relative importance. </li></ul><ul><li>Posterior and anterior elevation maps were decomposed into Zernike polynomials using customized Matlab routines. </li></ul><ul><li>Root mean squared error (RMSE) high-order residual above the 2 nd Zernike order was calculated for the anterior, posterior , and the difference between them. </li></ul><ul><li>Extreme RMSE values of the astigmatic eyes were used as the screening criteria (i.e. 100% specificity). </li></ul><ul><li>Receiver Operating Characteristic (ROC) curve and the area under the curve ( AUC ) quantitatively describes relationship between detection sensitivity and specificity at different thresholds. </li></ul>
  4. 4. Results : 5mm High-Order RMSE FFKC (mild KC) Moderate KC Advanced KC Astigmatic <ul><li>Anterior missed 8 of the 18 (56% sensitivity); 5 FFKC, 2 moderate, and 1 advanced. </li></ul><ul><li>Posterior missed 6 of 18 eyes (67% sensitivity). </li></ul><ul><li>RMSE difference missed 5 of the 18 (72% sensitivity). </li></ul>
  5. 5. Results : 5mm ROC Curves <ul><li>Nearly all moderate and advance KC tests can be correctly identified (solid lines). </li></ul><ul><li>Posterior (green lines) and difference (red lines) metrics better distinguish moderate and advanced KC subjects than anterior (blue lines). </li></ul>
  6. 6. FFKC (mild KC) Moderate KC Advanced KC Astigmatic Results : 6mm High-Order RMSE <ul><li>Anterior missed 7 of the 18 (61% sensitivity); 5 FFKC, 1 moderate, and 1 advanced. </li></ul><ul><li>Posterior and the RMSE difference missed 6 of the 18 (67% sensitivity); 5 FFKC and 1 moderate KC. </li></ul>
  7. 7. Results : 6mm ROC Curves <ul><li>All metric classifiers better distinguish moderate and advance KC subjects (solid lines) than subjects with FFKC (dotted lines). </li></ul><ul><li>Anterior, posterior, and difference metrics similarly distinguish FFKC and KC from astigmatic subjects. </li></ul>
  8. 8. FFKC (mild KC) Moderate KC Advanced KC Astigmatic Results : 7mm High-Order RMSE <ul><li>Anterior missed 7 of the 18 (61% sensitivity); 5 FFKC, 1 moderate, and 1 advanced. </li></ul><ul><li>Posterior and the RMSE difference missed 4 of the 18 (78% sensitivity); 3 FFKC and 1 moderate KC. </li></ul>
  9. 9. Results : 7mm ROC Curves <ul><li>Posterior and difference HO RMSE metrics classify 63% of FFKC subjects, while anterior only classifies 38%. </li></ul><ul><li>FFKC detection sensitivity over a larger 7mm area is improved over the smaller areas (i.e. 5mm, 6mm). </li></ul>
  10. 10. Results : FFKC and KC Classification KC sensitivity at 100% specificity KC area under ROC curve FFKC sensitivity at 100% specificity FFKC area under ROC curve Anterior 5mm 70% 0.92 38% 0.67 Posterior 5mm 90% 0.99 38% 0.66 Difference 5mm 100% 1.00 38% 0.68 Anterior 6mm 80% 0.94 38% 0.69 Posterior 6mm 90% 0.98 38% 0.68 Difference 6mm 90% 0.97 38% 0.64 Anterior 7mm 80% 0.93 38% 0.75 Posterior 7mm 80% 0.97 63% 0.84 Difference 7mm 90% 0.95 63% 0.81
  11. 11. Conclusions : <ul><li>Posterior cornea surface alone provides more of a significant indication of keratoconus than the anterior surface. </li></ul><ul><li>Analysis with a larger cornea area improves detection sensitivity . </li></ul><ul><li>Neither anterior or posterior cornea irregularity by itself is a sufficient indicator of early KC , and sometimes additional information is required to clinically diagnose FFKC. </li></ul>

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