| Objectives:To approach the accuracy of introcular pressure(IOP) measured by Reichert Ocular Response Analyzer(ORA),to compare and analyze the relationship between central corneal thickness(CCT) and IOP value measured by ORA,Goldmann applanation tonometry(GAT) and dynamic contour tonometry(DCT).Then to study the clinical utility of the corneal hysteresis(CH) and corneal resistane factor(CRF) measured by ORA in normal and undergone kerato-refractive surgery subjects.Method:Chose 158 healthy individuals(296 eyes ) for IOP measuring from April to September in 2008 randomly.After CCT was measured by A-ultrasound(A-US),IOP was measured by ORA,GAT and DCT devices in random order.Then compared the measuring values of these three tonometries with each other and correlated them with CCT seperately.In addition,chose other 120 individuals(213 eyes) undergone kerato-refractive surgery into this study.CH,CRF and IOP cornealcompensated (IOPcc) were provided by the ORA device;compared to the IOP was measured by the GAT device,then the Pearson correlation of these parameters were analysed.Results:In normal subjects,IOP readings were 15.21±2.77mmHg with ORA,15.22±2.77mmHg with GAT and 15.49±2.71mmHg with DCT,the mean differences were 0.01±2.29mmHg between ORA and GAT(P>0.05),0.28±2.01mmHg between ORA and DCT(P>0.05), respectively.IOPcc correlated more significantly with GAT(r=0.854, p=0.000) than with DCT(r=0.946,P=0.000).DCT has significant correlation with GAT(r=0.854p=0.000).GAT remarkably correlated with CCT(r=0.271,P<0.001),while IOPcc showed weakly significant correlation with CCT(r=-0.155,p=0.007).There was a remarkably negative correlation between CCT and the difference of IOPcc and GAT. Every 10-μm increase of CCT would result in increase of this difference for 0.35mmHg.In the thicker cornea group(CCT>580μm),IOPcc correlated the wrost significantly with GAT(r=0.859,p=0.000);while in the thinner cornea group(CCT<520μm),there was the best significant correlation between IOPcc and GAT(r=0.926,P=0.000).However,in these three groups of different thickness of the cornea,the correlated differences between IOPcc and DCT were no significant(P>0.05).The mean value of CH and CRF among healthy individuals were 10.15±1.31mmHg and 9.78±1.75mmHg,respectively.While CH,CRF,IOPcc and GAT in individuals undergone kerato-refractive surgery were 7.33±0.39mmHg,6.00±1.58mmHg,14.14±2.44mmHg and 9.80±2.66mmHg,respectively.Corneal hysteresis was not strongly correlated with IOP or CCT.The mean CH in the undergone keratorefractive surgery group(7.33±0.39mmHg) was lower than normal groups (10.15±1.31mmHg).The lower of the CH,the lower of its correlation between IOPcc and GAT value.The CH was significantly higher than the CRF after undergone kerato-refractive surgery.The mean CH in low-myopia,moderate-myopia and high-myopia individuals undergone kerato-refractive surgery were 9.04±1.32mmHg,7.53±1.12mmHg and 6.36±1.13mmHg,respectively,and the difference among these three groups were statistically significant(P＜0.05).The mean CH in the LASIK group and the LASEK group were 7.80±1.23mmHg and 6.17±1.01mmHg,respectively,and the difference between these two groups was statistically significant(P＜0.05).The decreased value of GAT, IOPg,CH and CRF values between pre-operation and post-operation of kerato-refractive surgery were 3.47±2.27 mmHg,4.34±2.20 mmHg, 2.86±1.29 mmHg and 3.68±1.50 mmHg,respectively;while the decreased value of the IOPcc between pre-operation and post-operation of kerato-refractive surgery was only 0.55±1.94 mmHg(P=0.062)Conclusion:ORA has high repeatablility and can keep high accordance with GAT,moreover,it is affected by CCT moderately.The readings of ORA are much closer to real IOP than GAT probably, especially in eyes undergone kerato-refractive surgery.The CH,a new corneal parameter,has a moderate dependence on IOP and CCT.Weaker corneas could be screened with ORA parameters,and low CH could be considered a risk factor for underestimation of IOP.
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