arvo 2010 final

Does the Posterior Corneal Does the Posterior Corneal Elevation Provide the First Elevation Provide the First Indication of Keratoconus?Indication of Keratoconus?

K.C. Baker, Y.-L.Chen, L.Shi, J.W. L. Lewis, L.Kugler, K.C. Baker, Y.-L.Chen, L.Shi, J.W. L. Lewis, L.Kugler, M.Wang. M.Wang. Wang Vision Institute, Nashville, TN; Center for Laser Wang Vision Institute, Nashville, TN; Center for Laser Applications, University of Tennessee Space Institute, Applications, University of Tennessee Space Institute, Tullahoma, TN; Department of Ophthalmology, University Tullahoma, TN; Department of Ophthalmology, University of Tennessee, Memphis, TNof Tennessee, Memphis, TN

Program # 4963Poster # D759

PurposePurpose::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.

Subject MakeupSubject Makeup1. 18 KC and 22 astigmatic eyes were used during this study.

2. 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).

3. FFKC (i.e. mild KC) diagnosis relied on the other eye's condition from the same subject, other KC indications, and family history.

4. Astigmatic eyes all had a BCVA of 20/25 or better.

MethodsMethods::1. Analyze anterior and posterior elevation using Pentacam system to

evaluate their relative importance.

2. Posterior and anterior elevation maps were decomposed into Zernike polynomials using customized Matlab routines.

3. Root mean squared error (RMSE) high-order residual above the 2nd Zernike order was calculated for the anterior, posterior, and the difference between them.

4. Extreme RMSE values of the astigmatic eyes were used as the screening criteria (i.e. 100% specificity).

5. Receiver Operating Characteristic (ROC) curve and the area under the curve (AUC) quantitatively describes relationship between detection sensitivity and specificity at different thresholds.

ResultsResults: 5mm High-Order RMSE : 5mm High-Order RMSE

FFKC FFKC (mild KC)(mild KC)

Moderate Moderate KCKC

Advanced Advanced KCKC

AstigmaticAstigmatic

•Anterior missed 8 of the 18 (56% sensitivity); 5 FFKC, 2 moderate, and 1 advanced.

•Posterior missed 6 of 18 eyes (67% sensitivity).

•RMSE difference missed 5 of the 18 (72% sensitivity).

ResultsResults: 5mm ROC Curves: 5mm ROC Curves•Nearly all moderate and advance KC tests can be correctly identified (solid lines).

•Posterior (green lines) and difference (red lines) metrics better distinguish moderate and advanced KC subjects than anterior (blue lines).





ResultsResults: 6mm High-Order RMSE : 6mm High-Order RMSE •Anterior missed 7 of the 18 (61% sensitivity); 5 FFKC, 1 moderate, and 1 advanced.

•Posterior and the RMSE difference missed 6 of the 18 (67% sensitivity); 5 FFKC and 1 moderate KC.

ResultsResults: 6mm ROC Curves: 6mm ROC Curves•All metric classifiers better distinguish moderate and advance KC subjects (solid lines) than subjects with FFKC (dotted lines).

•Anterior, posterior, and difference metrics similarly distinguish FFKC and KC from astigmatic subjects.





ResultsResults: 7mm High-Order RMSE : 7mm High-Order RMSE •Anterior missed 7 of the 18 (61% sensitivity); 5 FFKC, 1 moderate, and 1 advanced.

•Posterior and the RMSE difference missed 4 of the 18 (78% sensitivity); 3 FFKC and 1 moderate KC.

ResultsResults: 7mm ROC Curves: 7mm ROC Curves•Posterior and difference HO RMSE metrics classify 63% of FFKC subjects, while anterior only classifies 38%.

•FFKC detection sensitivity over a larger 7mm area is improved over the smaller areas (i.e. 5mm, 6mm).

ResultsResults: FFKC and KC Classification: FFKC and KC ClassificationKC KC sensitivity sensitivity at 100% at 100% specificityspecificity

KC area KC area under ROC under ROC curvecurve

FFKC FFKC sensitivity at sensitivity at 100% 100% specificityspecificity

FFKC area FFKC area under ROC under ROC curvecurve

Anterior 5mmAnterior 5mm 70%70% 0.920.92 38%38% 0.670.67Posterior 5mmPosterior 5mm 90%90% 0.990.99 38%38% 0.660.66Difference Difference 5mm5mm

100%100% 1.001.00 38%38% 0.680.68


90%90% 0.970.97 38%38% 0.640.64


90%90% 0.950.95 63%63% 0.810.81

ConclusionsConclusions::

1. Posterior cornea surface alone provides more of a significant indication of keratoconus than the anterior surface.

2. Analysis with a larger cornea area improves detection sensitivity.

3. 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.

arvo 2010 final

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