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Article Type

Original Study

Abstract

Objective The aim of this study was to compare corneal hysteresis (CH) in normal and keratoconic corneas in high cylindrical astigmatism (≥3 D). Background There is a great interest in corneal biomechanics as it aids in the study of corneal viscoelasticity. The ocular response analyzer (ORA) measures the corneal biomechanics through the analysis of the corneal dynamic behavior when it is deformed by an air puff. Studies using ORA in the evaluation of corneal biomechanics revealed a significant difference between keratoconic and healthy corneas. Patients and methods This study included 22 normal and 24 keratoconic eyes, which were diagnosed by means of clinical examination and corneal pentacam topography. CH and corneal resistant factor were measured using ORA. Results The mean CH was found to be 10.92 ± 1.7 mmHg in normal individuals, whereas in keratoconic patients it was 7.7 ± 1.29 mmHg. However, the corneal resistance factor (CRF) was 11.077 ± 1.96 mmHg in normal individuals compared with 6.3 ± 1.59 mmHg in keratoconic patients. The difference between the normal and affected groups was statistically significant in both CH and CRF (P < 0.0001, independent sample t-test). A strong direct correlation of central corneal thickness (CCT) with CH and CRF was found. The correlation coefficients (r) were 0.729 and 0.793 with CH and CRF, respectively. Conclusion CH and CRF were significantly higher in normal eyes than in keratoconic eyes. The correlation of CCT with CH and CRF when assessing the corneal biomechanics showed that lower CH and CRF implies a significantly reduced viscoelastic response in keratoconus than in normal eyes. Thus, this weakness in corneal viscoelasticity is associated with the lower CCT identified in keratoconus eyes.

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