Effect Of Corneal Diameter On Preoperative Screening Results Of Corneal Refractive Surgery

Purpose: To investigate the effects of different corneal diameters on corneal morphology and corneal biomechanics during preoperative screening of corneal refractive surgery.Method: A retrospective series of case studies included 240 patients who were treated in the corneal refractive center of the second hospital of Jilin University from September 2019 to September 2020.All patients had no history of keratoconus and corneal surgery.The corneal diameter measured by Pentacam was divided into three groups: small corneal diameter group（60 eyes）with corneal diameter less than or equal to 11.1 mm,normal corneal diameter group（287 eyes）with corneal diameter greater than 11.1 mm and less than or equal to 11.8 mm,and large corneal diameter group（133 eyes）with corneal diameter greater than 11.8.Corneal thickness,BAD-D 、 Df 、 Db 、 Dp 、 Dt 、 Da and other corneal morphological parameters were measured by Pentacam in all patients.Corvis ST was used to measure corneal biomechanical parameters such as HCR,DA,SSI,INR,b IOP,HCd Arc Length,ARTH,SP-A1,CBI and TBI.Using SPSS 26.0 carry out statistical analysis on the test data and draw corresponding charts.When the data meet the two standards of standard normal distribution and square difference homogeneity,one-way ANOVA is used for statistical comparison.When the data do not meet the conditions of positive distribution or variance homogeneity,Kruskal Wallis H test is used.If the P value is less than 0.05,it is considered to be statistically significant.Correlation analysis was used to explore the correlation between corneal diameter and corneal topography and corneal biomechanical parameters.Results:（1）The results showed that there was no significant difference in ISV,IHA,IVA,IHD,KI and Dt between the groups,the other parameters Db（H=76.41）,BFSf（F=42.48）,BFSb（F=30.24）,Df（F=14.91）,Dp（F=31.43）,Da（F=9.88）,D（F=59.37）,PPIavg（F=31.62）,and ARTmax（F = 11.05）had significant differences among the groups with different corneal diameters.For the corneal topography parameters of different corneal diameter groups with different components,the pairwise comparison shows that there are statistical differences in BFSf,BFSb,Db,Dp,D,and PPIavg between any two groups.There is no statistical difference in Df,Da and ARTmax between a small cornea and a normal corneal,and there are statistical differences in Df,Da and ARTmax between a small corneal and a large corneal,normal corneal and large corneal.（2）There were no significant differences in corneal biomechanical parameters HCR,DA,SSI,INR,b IOP,A1 L,A2L,A1 V,A2V,ICR,DAratio and INR among the groups,while there were significant differences in PD（F=4.21）HCd Arc Length（F=10.00）,ARTH（F=47.86）,SP-A1（F=9.03）,CBI（F=37.80）,TBI（F=31.54）.The biomechanical data with statistical differences between the two groups were compared and analyzed.The results showed that there was no statistical difference in various parameters between the small corneal group and the normal corneal group,there was a statistical difference in PD,HCd Arc Length,ARTH,CBI,and TBI between the small corneal group and the large corneal group,and there was no statistical difference in SPA1 between the two groups.There were significant differences in other parameters between the two groups except PD.（3）Correlation analysis between corneal diameter and corneal topography showed that ISV,IHA,IVA,IHD,KI and Dt had no correlation with corneal diameter,all other parameters were correlated with corneal diameter,BFSf（r=0.43）and BFSb（r=0.36）were positively correlated with corneal diameter,Df（r=-0.25）,Db（r=-0.45）,Dp（r=-0.38）,Da（r=-0.20）,D（r=-0.49）,PPIavg（r=-0.38）,ARTmax（r=-0.21）were negatively correlated with corneal diameter.（4）The correlation analysis between corneal diameter and corneal biomechanics showed that A1 L,A2L,A2 V,HCR,DA,ICR,SSI,DAratio,INR,SP-A1 had no correlation with corneal diameter.A1V（r=-0.11）,HCd Arc Length（r=-0.15）,CBI（r=-0.24）,b IOP（r=-0.11）,TBI（r=-0.28）had a negative correlation with corneal diameter,PD（r=0.14）,ARTH（r=0.34）had a positive correlation with corneal diameter.Conclusion: 1.Corneal diameter has an impact on the preoperative screening of corneal refractive surgery.The smaller the corneal diameter,the greater the impact on the corneal topography BAD system.Therefore,the influencing factor of corneal diameter should be considered when using corneal topography to screen keratoconus before surgery.2.There is no significant difference in biomechanics between patients with small corneal diameter and normal corneal diameter.Therefore, corneal biomechanics can be used to solve the problem of false positive results caused by small corneal diameter.3.The preoperative examination of corneal refractive surgery should not only consider corneal morphology or corneal biomechanics alone.The combination of corneal topography and corneal biomechanics may be more accurate.