Study On Measurement Of Intraocular Pressure And Influence Factors Before And After Laser In Situ Keratomileusis

Purpose:To study the changes of intraocular pressure,central corneal thickness,corneal curvature,equivalent spherical degree（SE）,corneal hysteresis（CH）and corneal resistance factor（CR）before and after Laser Assisted In-situ KeratomiLeusis（LASIK）in adult myopia and their influences on the values of different intraocular pressure measurement instruments.Methods:（1）From June 2013 to October 2018,118 adult myopic patients（235 eyes）who underwent Femtosecondexcimer laser in situ keratomileusis（LASIK）in Chongqing Mingda Ophthalmological Clinic were selected to analyze the preoperative clinical data.Preoperative clinical data collected:IOP_NCT was collected by Non-contact tonometer,IOP_Schiotz was collected by Schiotz contact tonometer,IOPcc andIOPg were collected by Ocular response analyzer（ORA）,and IOP_DCTCT wascollected by DCT.Age and sex of patients were also collected.SE and Km values,CCT and AXL ORA were measured by comprehensive optometer and corneal topography,and CCT and AXL were measured by A ultrasonography.Corneal hysteresis（CH）and Corneal Resistance Factor（CRF）were collected by ORA.Preoperative Km value,SE,CCT,AL,CH and CRF were used to analyze the relationship with preoperative IOP_NCT,IOP_Schiotz,IOPcc,IOPg andIOP_DCT,respectly.（2）The preoperationandpostoperationclinical data of 118 adult myopic patients（235 eyes）were collectedandanalyzed.The Km value,SE,CCT,CH,CRF and IOP_NCT,IOP_Schiotz,IOPcc,IOPg,IOP_DCT were observed one month after LASIK and compared with LASIK before and after LASIK.IOP_NCT,IOP_Schiotz,IOPcc,IOPg,IOP_DCT intraocular pressure changes and The influence factors suchasKm value,SE,CCT,CH,CRF were studied retrospectively before and after LASIK toanalyzethe relationship.Results:1.The average age of 235 eyes of 118 myopic patients was 25.77（+8.06）years.The preoperative eye parameters were as follows:average SE was（-6.03±3.17）D,average AXL was（25.89±1.47）mm,Km was（43.47±1.44）D,average CCT was（541.76±34.42）um,average CH was（10.30±1.33）mmHg,average CRF was（10.03±1.64）mmHg.Intraocular pressure measurements:NCT was（13.11±2.50）mmHg,Schiotz tonometer was（12.81±2.24）mmHg,IOPg and IOPcc were（15.35±2.51）mmHg and（14.58±3.02）mmHg respectively before ORA measurement,and DCT measurements were（16.44±2.03）mmHg before ORA measurement.2.The correlation analysis showed that NCT measurements were positively correlated with CT,CH and CRF,negatively correlated with Km and not with SE.Schiotz measurements were positively correlated with CT,CH,CRF and negatively correlated with AXL and SE.DCT measurements were not significantly correlated with the above factors,suggesting that the above parameters had little or no effect on the preoperative DCT measurements;IOPcc measurements of ORA were positively correlated with CT,CH,CRF,and negatively correlated with Km.IOPg of ORA is positively correlated with CT,CH and CRF.3.Multivariate linear regression analysis showed that Km,CCT,CH and CRF were independent influencing factors of NCT,and the regression coefficients were positive,while NCT was not related to AXL and SE.It suggested that NCT measurements increased with the increase of Km,CCT,CH and CRF,but the change of AXL and SE had no effect on NCT.By comparing the standard regression coefficients,we found that CRF was the most important influencing factor of NCT measurements.Factor.AXL,SE,CCT,CH and CRF are independent influencing factors of Schiotz contact tonometer.The regression coefficients of AXL and SE are negative,while the Schiotz measurement values are independent of Km.It is suggested that the Schiotz measurement values increase with the increase of CCT,CH and CRF,but decrease with AXL and SE,and are less affected by Km.By comparing the standard regression coefficients,CRF is found to be the most important influencing factor of Schiotz measurement values.The independent influencing factor of DCT is only CRF,and the correlation coefficient is positive,which has nothing to do with other parameters.It is suggested that the measured value of DCT in this regression model is relatively only affected by CRF,and the measured value of DCT increases with the increase of CRF.The independent influencing factors of IOPcc and IOPg were CH and CRF,suggesting that IOPcc and IOPg increased with the increase of CH and CRF in this regression model.Compared with standard regression coefficients,CRF was the most important influencing factor of IOPcc and IOPg measurements.4.According to the size of AXL,the patients were divided into three groups:group A（AXL<24mm）,group B（24 mm≤AXL<26um）,and group C（AXL≥26mm）.The Schiotz measurements of group A,B and C were（13.21±0.43）mmHg,（12.41±1.98）mmHg,（12.15±2.50）mmHg,respectively,suggesting that with the increase of AXL,the Schiotz measurements gradually decreased.The measured values of IOPcc in group A,B and C were（13.94±2.92）mmHg,（15.11±2.54）mmHg and（15.86±2.32）mmHg,respectively,suggesting that the measured values of IOPcc increased with the increase of AXL,and there was a significant difference between groups.5.According to the size of SE,patients were divided into three groups:group A（SE<3D）,group B（-3D≤SE<6D）and group C（SE≥6D）.The Schiotz measurements in group A,B and C were（13.27±2.30）mmHg,（12.56±1.64）mmHg,（12.47±2.28）respectively,suggesting that with the increase of SE,the Schiotz measurements gradually decreased,and there was a significant difference between the groups.The IOPcc measurements of group A,B and C were（14.50±3.33）mmHg,（14.95±2.44）mmHg and（15.94±2.44）mmHg respectively,suggesting that the IOPcc measurements increased with the increase of SE,and there was a significant difference between groups.6.According to the size of Km,patients were divided into five groups:A group（Km<42D）,B group（42.0≤Km<43D）,C group（43D≤Km<44D）,D group（44D≤Km<45D）and D group（Km≥45D）according to the size of Km.NCT measurements in the five groups were（13.20±2.64）mmHg,（13.86±2.04）mmHg,（14.04±3.07）mmHg,（12.70±2.70）mmHg,（12.77±1.77）mmHg,Group B The intraocular pressure measurements were significantly higher than those in D and E groups,but further observation showed that the CCTs in the five groups were（545.91±35.71）um,（548.18±39.86）um,（549.19±30.46）um,（529.57±31.68）um,（536.79±31.15）um,respectively.It was found that the CCTs in A,B and C groups were similar,while those in D and E groups were higher than those in D,B and C groups,while those in A,B and C groups increased with the increase of Km and E groups.It increased with the increase of Km.Explanation:At the same CCT level,NCT measurement value increases with the increase of Km,but the influence of Km on NCT measurement value is less than that of CCT.7.According to the size of CCT,the patients were divided into four groups:group A（CCT<500 um）,group B（500 um≤CCT<540 um）,group C（540 um≤CCT<580 um）,and group D（CCT≥580 um）.The measured values of NCT in five groups were（11.20±0.97）mmHg,（12.07±1.37）mmHg,（13.79±2.66）mmHg,（15.32±2.81）mmHg,and the measured values of Schiotz in five groups were（11.16±2.12）mmHg,(12.44±1.91mmHg,（13.31±2.27）mmHg,（13.61±2.22）mmHg,and IOPg in the five groups were（13.57±2.37）mmHg,（13.61±3.01）mmHg,（15.02±2.95）mmHg,（16.68±3.48）mmHg,respectively.With the increase of CCT,NCT,Schiotz and IOPg showed an increasing trend,and the variance analysis showed significant difference between the groups（P<0.05）,while there was no significant difference between DCT and IOPcc groups（>0.05）.It is suggested that the measured values of NCT,Schiotz and IOPg increase with the increase of CCT,and there is a significant difference between groups,but CCT has no effect on DCT and IOPcc.8.According to the size of CH,patients were divided into three groups:A group（CH<9.5 mmHg）,B group（9.5 mmHg≤CH<12.3mmHg）,Cgroup（CH≥12.3mmHg）.The measured values of IOPcc in the three groups were（13.78±3.14）mmHg,（14.56±2.79）mmHg,（17.00±3.02）mmHg,respectively.The measured values of IOPcc in the three groups were（16.30±2.63）mmHg,（15.04±2.35）mmHg,（14.85±2.69）mmHg,but there was no significant difference among DCT groups（P>0.05）.It is suggested that with the increase of CH,the measured values of NCT,Schiotz and IOPg gradually increase,while the measured values of IOPcc decrease.There is a significant difference between the two groups（P<0.05）.The measured values of DCT are relatively unaffected by the change of CH.9.According to the size of CRF,patients were divided into three groups:group A（CRF<8.9 mmHg）,group B（8.9≤CRF<12.1 mmHg）,and group C（CRF≥12.1 mmHg）.NCT measurements in the three groups were（11.17±1.06）mmHg,(11.17±1.06 mmHg,（13.14±2.21）mmHg,(13.14±2.21 mmHg,(13.14±2.21 mmHg,（13.14±2.21）mmHg,（16.76±2.16）mmHg,Schiotz measurements were（11.03±1.46）mmHg,（13.07±2.11）mmHg,（14.7±2.11）mmHg.There were significant differences between the two groups（P<0.05）,but there was no difference between the DCT measurements（P>0.05）.It is suggested that with the increase of CRF,NCT,Schiotz,IOPcc and IOPg show an increasing trend,while DCT measurement is relatively unaffected by the change of CRF.10.Km,SE,CCT,CH and CRF decreased significantly after femtosecond laser LASIK（P<0.01）.Km decreased（5.48±2.33）D after LASIK,SE decreased（6.21±3.01）D after LASIK,CCT decreased（105.50±34.35）um,CH decreased（2.20±1.63）mmHg,CRF decreased（3.58±1.66）mmHg.Among the five intraocular pressure measurements,the change of intraocular pressure measurements and the order of change ranges were the smallest in DCT from small to large,which were（1.54±2.75）mmHg（amplitude 9.37%）,IOPcc（2.31±2.89）mmHg（amplitude 15.05%）and Schiotz（3.38±2.12）mmHg.（range 26.39%）and NCT（3.77±2.47）mmHg（range 28.76%）.The largest decrease was IOP（5.42±3.47）mmHg（range 37.17%）of ORA,suggesting that changes in corneal parameters had the smallest impact on DCT,DCT measurement was the most accurate,and IOPg measurement was the most inaccurate.11.In order to observe the influence of CCT on various intraocular pressure measurements,63 eyes were screened out from all the cases received CCT measurements before and after operation,and the factors such as Km,SE,CH and CRF were controlled.According to the corneal thickness after operation,there were three groups:group A（CCT<400micron）（n=20）,group B（400 micron<CCT<450 micron）（n=23）,group C（CCT<450 micron）（n=20）,and group C CCT<450 micron（n=20）,respectively.Group A:CCT（<400 um）and group B（<450 um）were higher than those of thin central corneal thickness group(CCT<400 um in group A and 400 um（<450 um in group B）.There were significant differences in post-operative measurements of NCT,Schiotz,IOPcc and IOPg between different CCT groups（P<0.05）,while there was no significant difference in post-operative measurements of DCT between different central corneal thickness groups（P>0.05）.It is suggested that the measurement of NCT,Schiotz,IOPcc and IOPg increased with the increase of CCT,excluding the influence of Km,SE,CH and CRF after operation,but CCT had no significant effect on DCT after operation.12.In order to observe the effect of Km on various intraocular pressure measurements,96 eyes were screened out from all the cases received intraocular pressure measurements before and after operation.CCT,SE,CH,CRF and other factors after operation were controlled.According to Km after operation,there were three groups:group A（Km<37.5D）,group B（37.5D<Km<38.5D）,and group C（Km<38.5D）.There was no statistical difference in the measured values among the groups（P>0.05）.It is suggested that all kinds of measurement methods are not affected by Km changes.13.The correlation analysis indicated that IOP_NCT was correlated with Km,CCT,SE,CH and CRF one month after femtosecond laser LASIK（P<0.05）,in which IOP_NCT was highly positively correlated with CRF（r=0.351,P<0.001）.One month after operation,IOP_Schiotz was correlated with Km,CCT,SE,CH and CRF（P<0.05）.One month after operation,IOPcc was correlated with Km,CCT and SE（P<0.05）,and highly correlated with CH,CRF and IOPcc（r was-0.246 and 0.363,P<0.001）,respectively.IOPg was positively correlated with Km,CCT,SE,CRF and IOPg one month after operation（P<0.001）.14.After femtosecond laser LASIK,corneal curvature,equivalent sphericity,central corneal thickness,corneal hysteresis and corneal resistance factor were significantly decreased（P<0.01）,Km decreased（5.48<2.33）D,SE decreased（6.21<3.01）D,CCT decreased（105.50<34.35）um,CH decreased（2.20<1.63）mmHg,CRF decreased（3.58<1.66）mmHg.Postoperative intraocular pressure measurementsConclusions:1.DCT is more accurate than NCT,Schiotz,IOPcc and IOPg in myopic adults.Compared with other measurement methods,DCT is not affected by AXL,Km,SE,CCT,CH and CRF.When measuring NCT,the influence of patients’CCT,Km and other factors should be taken into account.The increase of Km can change CH and CRF,and then lead to the increase of NCT measurement value.Excluding the influence of CCT,CH and CRF,the change of Km has no effect on NCT.Schiotz tonometer is affected by the eyewall hardness.The eyewall hardness of patients with high myopia decreases,and the measured value will be low.Therefore,it is necessary to avoid using Schiotz tonometer when measuring the intraocular pressure of patients with high myopia.IOPcc is relatively unaffected by CCT.When patients have abnormal CCT,such as thinner or thicker CCT,ORA can be considered for IOPcc.Preoperative IOPg is closely related to GAT,which is close to the true intraocular pressure,but IOPg is greatly affected by CCT and corneal biomechanical properties.2.After femtosecond laser LASIK,the IOPg of ORA and DCT decreased the least,and the IOPg of ORA decreased the most.Postoperative DCT measurements are less affected by changes in SE,CCT,CH and CRF than NCT.DCT measurements can be the first choice for corneal refractive surgery before and after surgery.However,there may be a critical value of CCT changes,which makes DCT measurements significantly changed.The change of corneal curvature itself does not change corneal thickness and does not really have the biomechanical properties of cornea.However,the cornea with high curvature has the advantage of shape and structure compared with the cornea with low curvature when the ORA pulse airflow impacts.However,under the same thickness of CCT,the resistance of cornea with higher curvature to external force is comparable to that of cornea with lower curvature.It is only the increase of corneal biomechanical parameters measured by ORA.Postoperative NCT correction of intraocular pressure:actualIOP_NCT=IOP_NCT-post+0.701*IOP_NCT-pre-0.314*ΔCH+0.334*ΔCRF+0.109*△Km-6.78。Postoperative Schiotz correction of intraocular pressure:actual IOP_Schiotz=IOP_Schiotz-post+0.547*IOP_Schiotz-pre+0.226*ΔCH+0.305*ΔCRF-5.251.