Corneal resistance factor may outperform corneal hysteresis in detecting keratoconus

Issue: August 25, 2012

Upon consideration of central corneal thickness and biomechanical testing, keratoconic corneas were better detected by corneal resistance factor than by corneal hysteresis, a study found.

The observational case series compared 77 eyes with keratoconus and 102 healthy eyes. Analysis included corneal topography, tomography and biomechanical testing using the Ocular Response Analyzer (ORA, Reichert Technologies). Central corneal thickness (CCT), corneal hysteresis (CH), corneal resistance factor (CRF) and diagnostic performance of CH and CRF were the primary outcome measures.

Study results indicated that CH was 9.79 mm Hg in the control group vs. 8.49 mm Hg in the keratoconus group (P < .0001), while CRF was 9.55 mm Hg in the control group and 7.24 mm Hg in the keratoconus group (P < .0001). Only CRF remained significantly lower in eyes with keratoconus after CCT stratification. In keratoconic eyes with normal topography, the true positive rate for CRF was 84%.

“It seems CRF, but not CH, is a reliable indicator of abnormal biomechanics in eyes with keratoconus, even for subclinical cases with unremarkable topography, but only if corneal thickness is taken into account,” the study authors said. “We have derived both optimized CRF cutoff values and transformed indices for this purpose and believe that ORA testing should be considered in the preoperative screening of LASIK candidates.”

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Source:

J Refract Surg. 2012;28(3):202-208.