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RESEARCH PRODUCT

Are Ocular Response Analyzer useful to measure corneal hysteresis in patients with intracorneal rings?

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Purpose Corneal hysteresis is a viscoelastic property characterized by the difference in behavior under loading and unloading. The aim of the study was to determine corneal hysteresis in different eyes: healthy eyes, keratoconic eyes and keratoconic eyes after intracorneal ring implants. Methods This study comprised 95 eyes of 59 patients. The study population was divided into 3 groups. We analyze 30 healthy human eyes, 35 keratoconic eyes (Amsler grade II-III) and 30 keratoconic eyes after intracorneal rings implantation. Corneal biomechanical properties of these eyes were measured with the Ocular Response Analyser (ORA-Reichert) according to two parameters: corneal hysteresis (CH) and corneal resistance factor (CRF. The unpaired T student test was used for statistical analysis. Results Mean CH and CRF in normal eyes (10.78 ± 1.6 (SD) mm Hg, 11.91 mm Hg ± 1.2) was clearly superior than in keratoconus group (8.01 ± 1.5 mm Hg, 7.32 ±1.8 mm Hg). However the difference of these parameters between keratoconus group without intracorneal rings and after corneal ring implantation (7.27mm Hg, 6.32 mm Hg) was not statistically significant (p ≤ 0.01). Mean follow-up period was of one year. Conclusion Corneal hysteresis and CRF values were significantly lower in keratoconic eyes than in normal eyes. But there is no marked differences if we compare these two biomechanical parameters in keratoconic corneas, before and after corneal ring implants. Improvements in the software accuracy of the ORA devices are needed to characterize corneal biomechanics.