Investigation the relationship between biomechanic properties of cornea and refractive errors

PURPOSE: Corneal Hysteresis (CH) and Corneal Resistans Factor (CRF)are two corneal biomechanical parameters which were measured by ORA.Major aim of this study was to define the corneal CH and CRF in the myopicand hypermetropic patients and investigate the effectiveness of theseparameters on intraocular pressure measurement and compare the resultswith emmetropic control group.MATERIAL AND METHODS: 193 eyes of 100 healthy volunteers wererecruited. Study groups were recruited as; high myopia patients (n=27) withspheric refractive errors (SRE) of greater than -5.00 D, high hiperopiapatients (n=20) with SRE of greater than +3.00 D and controls (n=53) withSRE between ±1.00 D. All subjects underwent IOP and cornealbiomechanical evaluation with the ORA. Also Goldmann applanationtonometry, central corneal thickness (CCT), corneal curvature and axiallength measurements were performed.RESULTS: Mean age of groups were 30.7±6.9, 29.1±7.7, 28.9±5.6 yearsrespectively, statistical difference was not significant (p>0.05). Among studygroups except CRF and CCT, all parameters were significantly differentbetween study groups. CH was lowest in the high myopia group and highestin the high hypermetropia. In all groups, there were significant correlationsbetween CH and CRF, CCT, SRE, SE, AL and between CRF and CCT. GATand IOPg measurements were significantly correlated with CCT, whereasIOPcc measurements were not. The difference between GAT and IOPccmeasurements was significantly influenced by corneal thickness, AL, CH andCRF. Similarly the difference between IOPg and IOPcc measurements wassignificantly influenced by CRF, CH, CCT and AL. One of the major findingswas; as the CH approachs to 11.2 mmHg, IOPcc and IOPg get close to eachother. Meanwhile, the closest average CH values to 11.2 mmHg wererecorded in hyperopia group. The difference between GAT and IOPgmeasurements was significantly influenced by corneal thickness and CRF.61CONCLUSIONS: The results indicate that some compromised aspects ofthebiomechanical properties of cornea may exist in people. Results revealedthat, CRF, unlike to CH, is not affected from refractive errors and IOPcc isnot affected from any other ocular parameter. The difference between IOPccand IOPg was greatest in myopia group and IOP measurement in thesepatients deserve high suspicion.