The Reasearch Of Posterior Corneal Astigmatism In The Patients With Cataract

Part one The distribution of posterior corneal astigmatism in cataractpatients.Objective: To study the distribution of posterior corneal astigmatism inthe patients with cataract.Methods:Nine-four eyes undergoing phacoemulsification were measuredwith a rotating Scheimp camera（Pentacam;Oculus Inc,Wetzlar,Germany）preoperative.According to the outcome of Pentacam, we would study thedistribution of. posterior corneal astigmatism.Results: The mean posterior corneal astigmatism（PCA） was（0.34±0.21）D，40eyes （42.6%） had a PCA＜0.30D,37eyes（39.4%）between0.30D to0.50D,another17eyes （18.1%）≥0.5D. The mean axis of PCA was88.32°±23.10°, in these eyes,88eyes（93.62%）had the PCAwith the rule（WTR）,4eyes （4.26%） against the rule（ATR）,another2eyes （2.13%） wereobilque.There were no statistical correlations between the degree of PCA andage,gender（P＞0.05）.Significant correlations were found between the degreeof PCA and the degree of anterior corneal astigmatism（ACA）,（r=0.224，P=0.03＜0.05）,the higher of the degree of ACA, so was the PCA. We alsofound the correlations between the axis of PCA and ACA（r=0.255，P=0.014＜0.05）,the greater of the axis of ACA, so was the PCA.Conclusions: The degree of PCA was mostly low and with the axis WTR,there were significant statistical correlations between the degree and axis ofPCA and ACA, we could call this phenomenon “anastomosis” or “close”.Part two The influence of PCA to total corneal astigmatism（TCA）andobservation of PCA pre-and postoperative in the patients undergone3.2mm clear corneal incisional phacoemulsification with foldable IOLimplantation Objective: To observe the changes of PCA before and after3.2mm clearcorneal incisional phacoemulsification with foldable IOL implantation,cal-culate the TCA and evaluate it’s accuracy when neglecting PCA.Methods: The TCA was obtained according to the vectors calculation ofPCA and ACA in44eyes with cataract, then we would observe the differencebetween TCA and ACA.The44eyes were performed with phacoemulsification（bitamporal incision in right eyes, paranasal left eyes）, the changes of PCAbefore surgery and1day,1week,1month and3month after surgery werecompared.Results:The mean degree of ACA obtained by Pentacam was1.24±0.72D,the Pentacam-derived total corneal astigmatism（TCA） was1.13±0.72D,there was significant difference statistically between ACA andTCA（P＜0.05）. In the44eyes, it brought a mean reduction of0.30±0.18D in27eyes （61.36%）, a mean increase of0.18±0.14D in17eyes（39.64%） of TCAcompared with ACA. The mean degree of PCA1day,1week,1month and3month after surgery were0.680±0.370D，0.543±0.320D，0.430±0.320D，0.327±0.193D respectively, there was no significant difference statisticallybefore and3month after operation （t=0.211，P=0.834＞0.05）.Conclusions: The PCA showed a “rise-down” trend after3.2mm clearcorneal incision in phacoemulsification（bitamporal incision in right eyes,paranasal left eyes）without suture, when3month after surgery,there was nosignificant difference statistically compared with preoperative PCA. So thechanges of PCA after surgery was too small to be neglected. The PCA wouldbring a significant deviation in corneal astigmatism estimation in a proportionof eyes,so it could not be neglected.Part three The influence to cylindrical selection of Toric IOL whenneglecting the posterior corneal astigmatism.Objective：Demonstrate whether the Toric IOL options would change if weneglect the posterior corneal astigmatism.Methods: Two methods （TCA and ACA method）were used to calculate theToric IOL data （Acrysoftoriccalculator. com）,we observed the change of cylindrical data.Results: The mean astigmatism of TCA and ACA methods were1.57D±0.56D （range0.9D to3.7D） and2.01D±0.61D （range1.3D to4.3D）,theastigmatism of TCA and ACA group had statistically significant diffierence（P＜0.05）,3（5.26%）eyes IOL data were changed form T_n to T_n+1（for exampleT3-T4）,19eyes （33.33%） had no change,29eyes（50.88%） changed form T_ntoT_n-1,6（10.53%） from T_nto T_n-2,another7eyes’ corneal astigmatism became toolittle to be corrected.Conclusions: It brought a significant deviation in the selection of ToricIOL options when neglect the posterior corneal astigmatism in a proportion ofeyes.