Corneal Biomechanical Metrics and Anterior Segment Parameters in Mild Keratoconus
Received 23 February 2009; received in revised form 29 August 2009; accepted 14 September 2009. published online 05 February 2010. Corrected Proof
Purpose
To compare corneal hysteresis (CH), corneal resistance factor (CRF), spherical equivalent (SE), average central keratometry (K-Avg), corneal astigmatism (CA), corneal volume (CV), anterior chamber (AC) depth, and central corneal thickness (CCT) between patients with mild keratoconus and healthy controls and to estimate the sensitivity and specificity of CH and CRF in discriminating mild keratoconus from healthy corneas.
Design
Comparative case series.
Participants
Sixty-three eyes (40 patients) with mild keratoconus (group 1) and 80 eyes from 40 gender- and age-matched controls (group 2).
Methods
Patients underwent a complete clinical eye examination, corneal topography (Humphrey ATLAS; Carl Zeiss Meditec, Dublin, CA), tomography (Pentacam; Oculus, Wetzlar, Germany), and biomechanical evaluations (ocular response analyzer; Reichert Ophthalmic Instruments, Depew, NY). The receiver operating characteristic (ROC) curve was used to identify cutoff points that maximized sensitivity and specificity in discriminating mild keratoconus from normal corneas.
Main Outcome Measures
Corneal hysteresis, CRF, SE, K-Avg, CA, CV, AC depth, and CCT. The diagnostic performance of CH and CRF for detecting mild keratoconus was assessed using the ROC curve.
Results
In group 1 versus group 2, the SE values (mean±standard deviation) were –3.55±2.87 diopters (D) versus –1.46±3.09 D (P = 0); K-Avg, 45.09±2.24 versus 43.24±1.54 D (P = 0); CA, 3.15±1.87 versus 1.07±0.83 D (P = 0); CV, 57.3±2.12 versus 60.86±3.39 mm3 (P = 0); AC depth, 3.19±0.35 versus 3.05±0.43 mm (P = 0.0416); CCT, 503±34.15 versus 544.71±35.89 μm (P = 0); CH, 8.50±1.36 versus 10.17±1.79 mmHg (P = 0); CRF, 7.85±1.49 versus 10.13±2.0 mmHg (P = 0). The ROC curve analyses showed a poor overall predictive accuracy of CH (cutoff, 9.64 mmHg; sensitivity, 87%; specificity, 65%; test accuracy, 74.83%) and CRF (cutoff, 9.60 mmHg; sensitivity, 90.5%; specificity, 66%; test accuracy, 76.97%) for detecting mild keratoconus.
Conclusions
The values for CH, CRF, CV, and CCT were statistically lower and those for SE, K-Avg, CA, and AC depth were statistically higher in patients with mild keratoconus compared with controls. Corneal hysteresis and CRF were poor parameters for discriminating between mild keratoconus and normal corneas.
Financial Disclosure(s)
Proprietary or commercial disclosure may be found after the references.
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1Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil
2Centro de Microcirurgia e Diagnóstico, Rio de Janeiro, Brazil
ABSTRACT