Abstract
Purpose: :
To evaluate the biomechanical parameters measured by Ocular Response Analyzer (ORA) in intra-ocular hypertension (IOHT), open angle glaucoma (OAG) and normal subjects (NS), by comparing mean values and analyzing correlations, reliability and age influence.
Methods: :
Comparative study of 275 eyes from 145 subjects, divided in three groups: 64 IOHT, 46 OAG and 165 control patient eyes (NS). Following variables were compared: Goldmann applanation tonometry (GAT), central corneal thickness (CCT), and ORA derived parameters including: corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intra-ocular pressure (IOPg), and corneal compensated intra-oclar pressure (IOPcc). Statistical analysis used non-parametric tests and significant p value <0,05.
Results: :
The hignest mean CH was found in the NS group (10,2 +/-1,5), compared to IOHT (9,6 +/-2) and OAG (9,2 +/-1,8). The hignest mean CRF was observed in IOHT group (10,9 +/-2,1), compared to NS (10,1 +/-1,6) and OAG (9,9 +/-1,5). CH, CRF and CCT are well correlated with each other, whatever the group. CH is correlated with IOPcc and not with IOPg and GAT; inversely for CRF. In all groups, there is a good reliability between CH and CRF (r =0,49 to 0,77) and an strong reliability between IOPcc, IOPg and GAT (r =0,5 to 0,8). Whatever the group, CH and CRF present no influence of age, that confirms results of previous study. IOPcc is independant of CCT, strongly correlated (negatively) with CH, and statistically different between the three groups, IOHT, OAG and NS, results in agreement with previous published data. CH mean value is lower in OAG eyes, and statistically different compared to IOHT and NS, but there is an overlap of values between groups.
Conclusions: :
ORA derived corneal biomechanical parameters are not influenced by age. IOPcc is independant of CCT and seems to be a good estimation of intra-ocular pressure. CH and CRF significantly differ between OAG and normal eyes and appears to be useful for an earlier diagnosis of glaucoma.