Characteristics Of Corneal Asphericity And Posterior Corneal Astigmatism In Cataract Patients And Their Effect On Diopter Predictability

Aim:Cataract surgery has entered the era of refractive surgery.The main goal of the surgery is to improve visual quality while improving visual acuity.After the cloudy lens was removed,the main factor affecting the postoperative imaging quality of cataract patients is the characteristics of corneal morphology in addition to fundus function.Only with a fully understanding the characteristics of corneal morphological feature and its influence on cataract surgery can we design the appropriate operation and selection of appropriate intraocular lens according to the individual differences of patients.Corneal asphericity and corneal astigmatism reflect the irregularity of corneal morphology.Currently,there are relatively few studies on the characteristics of corneal asphericity and corneal posterior surface astigmatism in cataract patients and their impact on the prognosis of cataract surgery.Therefore,this study mainly focused on the characteristics of corneal asphericity and posterior corneal astigmatism in cataract patients before cataract surgery,and their effects on the refractive outcomes of cataract surgery,in order to provide a theoreticalbasis for the design of personalized surgical procedures and intraocular lens selection for cataract patients.Methods:This study was a retrospective study.The first part included 121 eyes of 121 cataract patients.The Q values of anterior and posterior corneal surfaces were measured by Sirius system in the 3.0mm,4.0mm,5.0mm and 6.0mm diameter ranges.Age,sex and corneal high-order aberration(HOA)were recorded.Correlation analysis was performed to evaluate the factors affecting corneal Q value.In the second part,121 eyes of 121 cataract patients were included.Sirius system was used to measure anterior corneal astigmatism(ACA),posterior corneal astigmatism(PCA),total corneal astigmatism(TCA),corneal aberration,corneal Q value and other anterior segment parameters.Lenstar LS 900 was used to measure the axial length.Correlation analysis and regression analysis were used to evaluate the correlation between PCA and other ocular parameters,including corneal Q value.In the third part,163 eyes of 163 cataract patients were included.The intraocular lens power was calculated by Barrett universal Ⅱ formula.Sirius was used to measure the Q values of the anterior and posterior surfaces of cornea in the diameter range of 3.0mm,4.0mm and 6.0mm before and after cataract surgery,and the PCA values in the diameter range of 3.0mm,5.0mm and 7.0mm.The changes of corneal Q value and PCA value before and after operation were compared by paired sample t-test.The relationship between prediction error of target diopter(i.e.the difference between target diopter and diopter measured one month after operation)and preoperative Q value,PCA valuewere evaluated by linear regression.The relationship between refractive error and Q value,PCA value were also evaluated by linear regression.Results:Part Ⅰ:The average Q value on the anterior surface of cornea were 0.09 ±0.42,0.02 ± 0.27,-0.04±0.20 and-0.11 ± 0.17in the range of 3.0mm,4.0mm,5.0mm and 6.0mm diameter,respectively.The average Q value of posterior corneal surface were 0.02± 0.81,-0.28 ± 0.56,-0.37 ± 0.43and-0.41 ± 0.30,respectively.The Q values of anterior and posterior corneal surfaces decreased with the increase of diameter measurement range.After grouping by age,the Q value of corneal anterior surface in the group≥ 70 years old(6.0mm diameter range)was significantly higher than that in the group aged 38～49 years old;The Q value of corneal posterior surface(4.0mm and 5.0mm diameter range)in≥ 70 years old group was significantly lower than that in 50-69 years old group;The Q value of posterior corneal surface in the group≥ 70 years old(6.0mm diameter range)was significantly lower than that of 38-49 years old group and 50-69 years old group.The Q values on posterior corneal surface were statistically significant between male and female groups in the range of 3.0mm,4.0mm,5.0mm and 6.0mm diameter.The Q value of anterior corneal surface in the range of 6.0mm diameter was positively correlated with total corneal spherical aberration,primary spherical aberration of the corneal front surface,trefoil aberration of the corneal front surface,total corneal aberration and total corneal HOA;The Q value of posterior corneal surface in the range of 6.0mm diameter was negatively correlated with coma aberration of the corneal back surface,and primary spherical aberration of the corneal back surface.Part Ⅱ:The average PCA of all cataract patients was 0.31±0.17D,and 85.9%of PCA was<0.5D.48.8%of ACA and 61.2%of TCA were with-the-rule astigmatism,while 86.0%of PCA were against-the-rule astigmatism.The astigmatic power vector(APV)of PCA was positively correlated with ACA,TCA and keratometric astigmatism(KA);PCA was positively correlated with total corneal spherical aberration,primary spherical aberration of the corneal front surface,total corneal aberration,total HOA and total low-order aberration;PCA was positively correlated with corneal Q value of anterior corneal surface in the diameter range of 6.0mm and 8.0mm.Part Ⅲ:There was no significant change in corneal Q value in 3.0mm and 4.0mm diameter one month after operation compared with that before operation,but there was significant difference in the Q value of anterior and posterior corneal surface in the diameter range of 6.0mm.The value of PCA(APV)in the diameter range of 3.0mm and 5.0mm was significantly different from that before operation,while there was no significant change in PCA(APV)value within 7.0mm diameter.Within the diameter range of 6.0mm,the corneal Q value and the change of corneal Q value before and after operation(ΔQ),whether on the anterior or posterior corneal surface,had no significant correlation with the prediction error of target diopter after implantation of different types of intraocular lens,including AcrySof IQ SN60WF,Tecnis ZCB00,Softec HD TM and Sensar AR40e.Within the diameter range of 5.0mm,the PCA(APV)value and the change value of PCA before and after operation(Δ PCA)also had no significant correlation with the prediction error of target diopter after implantation of the above four intraocular lenses.Neither Δ Q value nor Δ PCAwas correlated with uncorrected vision acuity after operation.The Δ Q value was positively correlated with spherical aberration,but not with total aberration and total HOA.In addition,there was no significant correlation between the Δ Q of posterior corneal surface and spherical aberration,total aberration and total HOA.ΔPCA was positively correlated with total aberration and total HOA,but not with spherical aberration.Conclusion:(1)There are great individual differences in corneal asphericity in cataract patients.When evaluating corneal asphericity,factors such as age,gender and HOAs should be considered.(2)Before cataract surgery,PCA value can be indirectly evaluated by corneal aberration and corneal Q value(especially anterior surface Q value).(3)After the intraocular lens power was calculated by Barrett Universal Ⅱ formula,neither the preoperative corneal Q value,PCA value nor Δ Q value,Δ PCA had effect on the prediction error of target diopter and postoperative visual acuity.(4)The change of Q value before and after operation affects the postoperative corneal spherical aberration.(5)The changes of PCA before and after operation affect the total corneal aberration and total HOA.