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Abstract
Purpose
To compare the biomechanical properties of keratoconus, keratoconus suspect, and normal subjects measured by ocular response analyzer.
Methods
A total of 72 patients were divided into 3 groups: keratoconus, suspected keratoconus, and normal control subjects. The 3 age-matched groups were evaluated according to age, sex, and visual acuity. Slit lamp examinations, Pentacam, and ocular response analyzer (ORA) examinations were performed. Mean corneal refractive power, central corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) were evaluated and analyzed.
Results
Twenty-four eyes were included in each group. The mean age was 23.8 years in keratoconus, 26.0 years in sus-pected keratoconus and 26.1 years in normal subject groups. Mean corneal refractive power was significantly higher in keratoconus (p < 0.001) and suspected keratoconus (p = 0.001) groups than in the normal subject group. Mean central corneal thickness showed significant differences among the 3 groups (p < 0.05). CH was significantly lower in keratoconus than suspected keratoconus (p = 0.025) and normal subject groups (p = 0.005), but showed no significant difference be-tween suspected keratoconus and normal subject groups. CRF showed significant differences among all 3 groups (p < 0.05). CH and CRF had negative correlations with mean corneal refractive power and positive correlations with central cor-neal thickness.
Conclusions
CH and CRF measured by ORA were significantly different between keratoconus and normal subject groups and had significant correlations with mean corneal refractive power and central corneal thickness. CRF may be a useful method to differentiate between suspected keratoconus and normal cornea patients.
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Figure 1.
Comparison of mean corneal refractive power (A) and central corneal thickness (B) among keratoconus, keratoco-nus suspect, and normal control groups. * Indicates a pair of groups that has a significant difference between each other with p < 0.05.
Figure 2.
Comparison of corneal hysteresis (A) and corneal resistance factor (B) among keratoconus, keratoconus suspect, and normal control groups. * Indicates a pair of groups that has a significant difference between each other with p < 0.05.
Figure 3.
Parameters significantly correlated with each other. (A: Corneal hysteresis (CH) to central corneal thickness (CCT), B: CH to mean corneal refractive power, C: Corneal resistance factor (CRF) to CCT, D: CRF to mean corneal refractive power, E: mean corneal refractive power to CCT, F: CH to CRF). A, C, F showed positive correlations and B, D, E showed negative correlations.
Figure 4.
The receiver operating characteristic (ROC) graph showing the sensitivity and specificity of the corneal hysteresis (A) and corneal resistance factor (B) for each pair of groups.
Figure 5.
Measurement of corneal hysteresis using Ocular Response Analyzer (Reichert Inc., Depew, NY). It is derived from the difference between the inward applanation and out-ward applanation.
Table 1.
Baseline characteristics of patients in keratoconus, keratoconus suspect, and control subjects
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