[A compare study on cornea biomechanical properties in normal and keratoconic eyes].

OBJECTIVE

To compare the corneal hysteresis (CH) and corneal resistance factor (CRF) measured with the Ocular Response Analyzer (ORA) in normal and keratoconic eyes.

METHODS

It was a case-control study. Random selected 96 normal eyes and 46 keratoconic eyes in the same period were included in this study. Normal eyes were divided into 2 groups: high corneal astigmatism (> or = 3.00 D) and low-to-moderate corneal astigmatism (< 3.00 D). Keratoconic eyes were also divided into 3 groups based on Amsler-Krumeich classification: mild (stage I), moderate (stage II) and severe (stage III/IV). CH and CRF were compared between groups and the areas under ROC curves of the CH and CRF were calculated.

RESULTS

The mean CH and CRF were (7.1 +/- 1.6) mm Hg and (6.3 +/- 1.5) mm Hg in keratoconic eyes compared with (10.1 +/- 1.3) mm Hg and (10.5 +/- 1.6) mm Hg in normal eyes. The difference were statistically significant(t = -11.813, -14.943; P < 0.001). In normal eyes, there was no difference of CH or CRF between the high corneal astigmatism and low-to-moderate corneal astigmatism (t = 0.373, 0.095; P > 0.05). In keratoconic eyes, there was a significant negative correlation between CH and the keratoconus grade (r = -0.627, P < 0.001) and the same relationship was found between CRF and the keratoconus grade (r = -0.587, P < 0.001). In multiple linear regression analysis,CH was correlated with central corneal thickness (CCT) and corneal curvature (r = 0.320, -0.375; P < 0.05) and CRF was correlated with corneal curvature in keratoconic eyes (r = -0.441, P < 0.01) , while they were only correlated with CCT in normal eyes (r = 0.367, 0.459; P < 0.001). The areas under ROC curves of the CH and CRF were 0.9282 and 0.9731 (Z = 20.462, 38.305; P < 0.0001), the difference between them was significant (Z = 7.134, P = 0.008).

CONCLUSIONS

The CH and CRF were significantly lower in keratoconic eyes than in normal eyes, especially on CRF. The long-term follow-up of CH and CRF may provide information for evaluation of progression of keratoconus. They may be included as indicators for detecting keratoconus.