الفهرس 
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Abstract
The aim of our study was To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in healthy eyes with a central corneal thickness (CCT) 470-500 μm with matched keratoconus (KC),keratoconus suspect (KCS)cases.
We used the Ocular Response Analyzer device which measures CH, CRF, IOPcc and IOPg compare it between our 3 group studies to study the changes in corneal biomechanics between theses groups with controlling the central corneal thickness ( 470-500 μm ).
Our study was performed on 66 eyes as we divided these patients into three groups. group 1 (Normal eyes ) involved 32 eyes with normal pentacam, group 2 (keratoconus suspect eyes ) involve 15 eyes with suspecious pentacam, group 2 (keratoconic eyes ) involve 19 eyes with keratoconus pattern in pentacam.
The corneal biomechanics in particular CRF are significantly higher in Normal group compared to keratoconus group as the mean CRF is 8.39 ± 1.47 mmHg in the group 1 (Normal) and is 8.27 ± 1.09 mm Hg for group 2 (keratoconus suspect) while It is 7.24 ± 1.27 mm Hg for group 3 (Keratoconus). The difference in CRF between the group 1 and 3 is statistically highly significant, (p value = 0.013),with no significant difference that could detect keratoconus suspect eyes. Meanwhile the mean CH is 8.55± 1.77 mmHg for group 1 (Normal) while It is 9.03± 1.119 mm Hg for group 2 (keratoconus suspect) and 8.06 ± 0.85 mm Hg for group 3(Keratoconus). the difference in CH between the three groups is statistically highly insignificant, (p value = 0.147).
Only the mean CRF was significantly lower in KC eyes compared to NL ones, but no significant difference was seen in CCT, CH and CRF parameters of KCS eyes compared with NL eyes,nor significant difference in CH parameter between the study groups.
CH and CRF are known to be highly correlated to corneal thickness As corneal thickness decreases significantly in keratoconic eyes. and usually is within NL limits in KCS and NL eyes, any changes in CH and CRF could be related to the changes in CCT. After controlling for the CCT in our study, only CRF differences between NL and KC remained significant.
The ORA parameters provided by ORA can be helpful in differentiating KC eyes from NL ones, but CH and CRF cannot detect KCS from NL eyes; therefore ORA alone would not be a helpful diagnostic tool for detecting KCS eyes.