Enhanced Combined Tomography and Biomechanics Data to Identify Forme Fruste Keratoconus

Saturday, April 18, 2015: 1:36 PM
Room 1B (San Diego Convention Center)
Allan Luz, MD
Bernardo T. Lopes, MD
Katie M. Hallahan, MD
Bruno F. Valbon, MD
Isaac C. Ramos, MD
Fernando Faria-Correia, MD
Paulo Schor, MD
William J. Dupps Jr, MD, PhD
Renato Ambrósio Jr, MD, PhD

To evaluate the performance of Ocular Response Analyzer (ORA) investigator derived variables and Pentacam HR tomographic parameters in differentiating forme fruste Keratoconus (FFKC) from normal corneas. To assess a combined biomechanical and tomographic parameter to improve outcomes.

Seventy-six eyes of 76 unaffected patients and twenty-one eyes of 21 FFKC patients matched for age, thinnest point, central corneal thickness and maximum keratometry from Instituto de Olhos, Rio de Janeiro, Brazil. Fifteen variables were derived from exported ORA signals to characterize putative indicators of biomechanical behavior, also thirty-seven ORA waveform parameters were tested. Sixteen tomographic parameters from Pentacam HR were tested.   Logistic regression was used to produce a combined biomechanical and tomography linear model. Differences between groups were assess by the Mann-Whitney test. The area under the receiver operating characteristics curve (AUC) were used to compare diagnostic performance.

Twenty-three of seventy-seven parameters showed significant differences between the FFKC and control group (Mann-Whitney test, p < 0.05).  Among the ORA waveform measurements, the best parameter were those related to the area under the first peak, p1area1 (AUROC, 0.717±0.065). Among the investigator ORA variables, a measure incorporating the pressure-deformation relationship of the entire response cycle was the best predictor (Hysteresis loop area (HLA), AUROC, 0.688±0.068). Among tomographic parameters BAD-D showed the highest predictive value (AUROC, 0.91±0.057). A combination of parameters showed the best result (AUROC, 0.953±0.024) outperforming individual parameters.

Tomographic and biomechanical parameters demonstrated the ability to differentiate forme fruste Keratoconus from normal eyes. A combination of both types of information further improved predictive value.