| ObjectiveTo investigate the distribution of anterior and posterior corneal astigmatism and the effect of posterior astigmatism(PA)on total astigmatism(TA)in all ages of normal corneal human;To study the effect of steep meridian clear corneal incision on anterior,posterior and total astigmatism of the cornea in cataract patients.MethodsA rotating Scheimpflug camera(Pentacam Oculus,Germany)was used to measure989 eyes of 571 patients who came to Tianjin Eye Hospital.The anterior astigmatism(AA)and PA was recorded.The distribution and correlation of AA and PA were summarized and the effects of PA on TA were analyzed.The simulated keratometry astigmatism(KA)was calculated by the anterior corneal surface measurement and the index of 1.3375,while TA was derived by anterior and posterior surface astigmatism and axial vector decomposition calculation.The clinical data of 63 patients with cataract surgery who came to Tianjin Eye Hospital from September to December 2017 were retrospectively analyzed and randomized into groups.In group A,30 patients in the observation group underwent cataract phacoemulsification and incision at the meridian of the anterior corneal surface at a steep incision;in group B,33 patients in the control group underwent transorbital(right eye)or upper nasal(left eye)clear corneal incision.Pentacam was used to performed before and 1 day,1 week and 1 month after cataract surgery in two groups.The measured anterior and posterior astigmatism and corneal curvature astigmatism were recorded.To sum up the effect of anterior,posterior and total astigmatism at different positions to the cornea.Results1.The mean PA was(0.34±0.16)diopters(D);The mean axis of PA was(87.59±65.72)°.with-the-role(WTR),against-the-role(ATR),oblique astigmatism of the posterior corneal surface was found in 345 eyes(34.8%),618 eyes(62.5%)and 26 eyes(2.6%);The mean AA was(1.22±0.75)diopters(D);The mean axis of AA was(89.88±63.70)°.with-the-role(WTR),against-the-role(ATR),oblique astigmatism of the posterior corneal surface was found in 363 eyes(36.7%),576 eyes(58.2%)and 50 eyes(5.1%)2.the magnitudes of AA and PA were significant correlation(Pearson correlation coefficient r=0.576,P<0.05).The axis of AA and PA were significant positive correlation(r=0.381,P<0.05).3.The magnitude of TA and KA were(1.21±0.76)D and(1.43±0.88)D,respectively,and there was significant difference(t=21.95,P<0.01).The axis of TA and KA were(89.88±63.70)°and(89.29±61.53)°,respectively,there was no significant difference(t=-1.08,P=0.28).4.The corrected vision of the patients in group A(0.32±0.19)before surgery and the corrected vision(0.86±0.21)at 1 month after operation were statistically significant;the vision of group B before surgery was(0.25±0.18)and the corrected vision(0.76±0.26)in the first month after surgery were statistically significant.The difference in visual acuity between the two groups was not statistically significant at 1 month after surgery(t=1.62,P=0.11).5.The anterior corneal astigmatism in group A was(0.51±0.38)in the first month after operation and the anterior astigmatism in group B(0.97±0.71)was statistically significant(t=-2.93,P<0.01).There was no significant difference in posterior corneal astigmatism between preoperative and 1 month after surgery in group A(t=1.10,P=0.28).There was no significant difference between preoperative and one month postoperative in group B(t=-0.27,P=0.79);Total corneal astigmatism in group A(0.66±0.42)at 1 month after surgery and in group B(1.10±0.75)have a statistically significant difference(t=-2.60,P=0.01).6.There was no significant difference in distribution of anterior corneal astigmatism axis at 1 month after operation compare with preoperative in group A and group B(all P>0.05).The posterior corneal with-the-rule astigmatism distribution in group A was statistically significant at 1 month after operation compared with preoperative(?~2=5.46.P=0.02).There was no statistically significant difference between against-the-rule astigmatism and oblique astigmatism(?~2=6.94,1.07,P=0.07,0.78);In Group B,the posterior corneal with-the-rule astigmatism and against-the-rule astigmatism were statistically significant at one month after surgery compared with preoperative(?~2=7.33,7.36,P=0.01,0.01),there was no statistically significant differencedistributionofobliqueastigmatism(?~2=1.82,P=0.61).Conclusion1.The diopter of PA was mostly low and mainly with the axis ATR.There were significant positive correlation between the magnitude and axis of PA and AA,the magnitudes of PA and TA were significant positive correlation,and PA can increase TA.If PA was neglected,there will lead to clinical significant inaccuracies in estimating of the corneal astigmatism.2.Both surgical incisions improved the patient's corrected visual acuity;the anterior corneal astigmatism in group A was significantly smaller than that in group B at 1month after surgery,but there was no significant change in the degree of posterior corneal astigmatism between the two groups.The change in total astigmatism of the cornea of the patient was basically consistent with the anterior corneal astigmatism;there was no significant change in the axial distribution of anterior corneal astigmatism between the two groups.The posterior corneal with-the-rule astigmatism of two groups decreased after surgery compared with preoperative,and there was an increase in against-the-rule astigmatism postoperative compared with preoperative,with little change in oblique astigmatism.This shows that corneal axial incision can significantly reduce the degree of anterior astigmatism,and the common incision increases anterior astigmatism,these two different incisions have little effect on the degree of corneal posterior astigmatism,but can make the posterior astigmatism axis from with-the-rule astigmatism to against-the-rule astigmatism. |
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