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Corneal biomechanical properties in normal, forme fruste keratoconus, and manifest keratoconus after statistical
R Duncan Johnson1, Myhanh T Nguyen, Nancy Lee
1Department of Ophthalmology, Cornea Division, Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Purpose:
To evaluate the difference in corneal biomechanical properties, after controlling for potentially confounding factors, along the spectrum of keratoconic disease as measured by the keratoconus severity score.
Methods:
The corneal biomechanical properties of 73 keratoconic (KCN) eyes of 54 patients, 42 forme fruste keratoconic (FFKCN) eyes of 32 patients, and 115 healthy eyes of 115 age- and sex-matched patients were reviewed retrospectively. The main outcome measures were corneal hysteresis (CH) and corneal resistance factor (CRF).
Results:
In the normal group, the mean CH was 11.0 ± 1.4 mm Hg and mean CRF was 11.1 ± 1.6 mm Hg. The FFKCN mean CH was 8.8 ± 1.4 mm Hg and mean CRF was 8.6 ± 1.3 mm Hg. The KCN mean CH was 7.9 ± 1.3 mm Hg and mean CRF was 7.3 ± 1.4 mm Hg. There were statistically significant differences in the mean CH and CRF in the normal group compared with the FFKCN and the KCN groups (P < 0.001) after statistically controlling for differences in central corneal thickness, age, and sex.
Conclusions:
There is a significant difference in the mean CH and CRF between normal and FFKCN corneas after controlling for differences in age, sex, and central corneal thickness. However, there is a significant overlap in the distribution of CH and CRF values among all groups. The biomechanical parameters CH and CRF cannot be used alone but may be a useful clinical adjunct to other diagnostic tools, such as corneal tomography, in distinguishing normal from subclinical keratoconic corneas.
