Enhanced Combined Tomography and Biomechanics Data for Distinguishing Forme Fruste Keratoconus

Abstract

PURPOSE To evaluate the performance of the Ocular Response Analyzer (ORA) (Reichert Ophthalmic Instruments, Depew, NY) variables and Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) tomographic parameters in differentiating forme fruste keratoconus (FFKC) from normal corneas, and to assess a combined biomechanical and tomographic parameter to improve outcomes. METHODS Seventy-six eyes of 76 normal patients and 21 eyes of 21 patients with FFKC were included in the study. Fifteen variables were derived from exported ORA signals to characterize putative indicators of biomechanical behavior and 37 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 assessed by the Mann–Whitney U test. The area under the receiver operating characteristics curve (AUROC) was used to compare diagnostic performance. RESULTS No statistically significant differences were found in age, thinnest point, central corneal thickness, and maximum keratometry between groups. Twenty-one parameters showed significant differences between the FFKC and control groups. Among the ORA waveform measurements, the best parameters 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, AUROC, 0.688 ± 0.068). Among tomographic parameters, Belin/Ambrósio display 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. CONCLUSIONS Tomographic and biomechanical parameters demonstrated the ability to differentiate FFKC from normal eyes. A combination of both types of information further improved predictive value.

Effect of accelerated corneal crosslinking on ocular response analyzer waveform-derived parameters in progressive keratoconus

“…Each parameter describes a morphologic feature of the waveform. Many studies have shown that these parameters are useful in distinguishing between keratoconus and normal patients, as well in identifying early and severe keratoconus (15)(16)(17) . Spoerl et al (18) showed a significant increase in p2 area, h2, and dive2 parameters at the one year follow-up after standard CXL treatment.…”

“…Although CXL has been shown to stabilize corneal biomechanics ex vivo (10)(11)(12) , this improvement in CRF and CH levels has not been demonstrated in vivo (13,14) . Numerous studies show that these second-generation parameters are more sensitive than the CRF and the CH in differentiating early-stage keratoconus from the normal cornea (15)(16)(17) . The new ORA software provides waveform-derived parameters and a more detailed analysis of the corneal deformation signal.…”

Biomechanical diagnostics of the cornea

“…Subsequently, the advent of anterior segment tomography, with the 3-dimensional reconstruction of the cornea, provided more detail about corneal architecture with a variety of quantitative indices derived from the front and back elevation and the pachymetric maps [3,14,21,22]. The ability of corneal tomography to further enhance the accuracy of detecting mild or subclinical ectatic disease was demonstrated in different studies involving eyes with typically normal topography from patients with clinical ectasia identified in the fellow eye [13,[23][24][25][26][27][28]. Such cases with regular topography from patients with very asymmetric ectasia (VAE-NT) represent the most important model for developing and testing novel diagnostic strategies for enhancing ectasia detection [14].…”

Evolution on Keratoconus and Corneal Ectatic Diseases: Paradigms and Paradoxes

“…37 Interestingly, the integration of corneal tomography and biomechanical assessments have been proposed to detect mild ectasia as well as to characterize ectasia susceptibility. 35,38 Eyes with normal front curvature (topometric) findings from patients with clinical ectasia detected in the fellow eye have been used to demonstrate the improved ability of advanced corneal imaging devices to detect mild ECD. [39][40][41] Klyce 42 referred to these cases to have forme fruste keratoconus, 42 a term coined by Amsler 43 in the early 1960s based on photokeratoscopy.…”