| Background:The purpose of this study was to investigate the early changes in corneal densitometry in patients who underwent SMILE(Small-incision lenticule extraction)surgery for correction of myopia,and to analyze the effects of related factors on corneal densitometry and the relationship between corneal densitometry and higher-order aberrations.MethodsThis study included a retrospective study of 110 patients(110 eyes)who underwent SMILE surgery at the refractive center of our hospital from July 2017 to April 2018 to correct myopia and corrected astigmatism.Patients underwent routine examinations before and 1 week,1 month,3 months and 6 months after SMLIE surgery.The examinations included all routine examinations were performed 6 months after surgery,including uncorrected visual acuity,diopter,and slit lamp examination.Pentacam three-dimensional anterior segment analyzer was used to measure corneal densitometry and higher-order aberrations.Changes in corneal densitometry and higher-order aberrations before and after surgery were observed.We analyzed the relationship between presurgical spherical equivalent,surgical parameters(central lens thickness,residual stromal thickness),postsurgical uncorrected visual acuity and corneal densitometry at the same period;We also analyzed the relationship between pre-equivalent spherical mirrors,spherical mirrors,cylinders,surgical parameters,and corneal high-order aberrations at different stages after surgery;In addition,we analyzed the relationship between corneal densitometry and corneal high-order aberrations at each postsurgical stage.The statistical analysis of the data was performed by SPSS 24.0 software.The Kolmogorov-Smirnov test was used to test the normality of each group of data.The Friedman test was used to analyze the changes of corneal densitometry before and after SMILE,the results were recorded as M(P25,P75).Single-factor repeated-measures analysis of variance was used to analyze the changes in the overall corneal high-order aberrations at various stages before and after surgery in the SMILE group.The results were recorded as mean±standard deviation(x±s).Pearson linear correlation analysis was used to analyze correlations between corneal densitometry and corneal high-order aberrations.Correlative analysis of corneal densitometry and corneal high-order aberrations was performed at each stage.P<0.05 was considered statistically significant.Result1.During the early follow-up,the patient’s uncorrected visual acuity gradually increased and became stable at 3 months after surgery.In 96.3%of the patients(106 eyes),the uncorrected visual acuity of the eyes reached 0.0 and below(LogMAR)6 months after surgery.2.The overall corneal densitometry had a significant difference before and after SMILE(χ2=33.786,P<0.001).There was a statistically significant difference in overall corneal densitometry between 1 week after surgery and presurgically,1 month postsurgically,3 months postsurgically,and 6 months postsurgically(χ2=33.786,P<0.001).There was no significant difference between the 6 months,3 months postsurgical and presurgical overall corneal densitometry(χ2=2.255,P=0.324).The average corneal densitometry after SMILE peaked at 1 week after surgery,and then gradually decreased until 3 months after surgery and was lower than the presurgical level.The overall corneal average optical density was stable from 3 months postsurgically to 6 months postsurgically.3.The difference of corneal densitometry in different diameter areas before and after surgery was statistically significant(χ2=81.020,P<0.001;χ2=80.721,P<0.001;χ2=14.846,P=0.002).The corneal densitometry in each region peaked at 1 week after surgery.The corneal densitometry in the 0-2mm and 2-6mm regions at 1 week after surgery was significantly higher than that before the surgery,and then gradually decreased and approached presurgical level at 6 months after the surgery.The 6-10mm region is similar to the 0-2mm and 2-6mm regions.The corneal densitometry in the 6-10mm region fell below the presurgical level at 3 months after surgery and was stabilized at 6 months after surgery.The average corneal densitometry of the areas of 0-2mm,2-6mm and 6-10mm regions were not significantly different between 3 months after surgery,6 months after surgery and before surgery(χ2=4.766,P=0.075;χ2=5.178,P=0.097;χ2=2.937,P=0.230).4.The corneal densitometry of different stratifications(first 120 μm,middle,and later 60 μm)were statistically different before and after surgery(χ2=5 3.904,P<0.001;χ2=14.381,P=0.002;χ2=19.599,P=0.001).The average corneal densitometry of each layer decreased gradually after peaking at 1 week after surgery,then the anterior layer fell below the presurgical level at 1 months after surgery,and the central corneal layer and the posterior corneal layer fell below the presurgical level at 3 months after surgery.It was close to the presurgical level at 3 months after surgery and further decreased at 6 months after surgery.The average corneal densitometry in the anterior corneal layer,the central corneal layer,and the posterior corneal layer was not significantly different after 3 months,6 months,and before surgery(χ2= 1.940,P=0.379;χ2=1.363,P=0.714;χ2=5.811,P=0.121).5.There was a significant postive correlation between the uncorrect visual acuity and total corneal densitometry at 1 week after surgery and 1 month after surgery((r=0.277,P=0.004;r=0.310,P=0.002).6.There was a weak negative correlation between the presurgical spherical equivalent and the total corneal densitometry at 1 week postsurgically(r=-0.200,P=0.038).There was a significant negative correlation between the presurgical spherical equivalent lens and the corneal densitometry of the anterior corneal layer at 1 week postsurgically(r=-0.261,P=0.007),and it was also significantly negatively correlated with the average corneal densitometry in the 2-6mm region at 1 week postsurgically(r=-0.236,P=0.014).There was a significant positive correlation between the central lens thickness and the average optical density of the layer cornea 1 week after surgery and 1 month after surgery(r=0.265,0.258;P=0.006,0.008).It was slightly negative correlated with the corneal average optical density of the 2-6mm region at 1 week after surgery,and 0-2mm,2-6mm region at 1 month after surgery,and the average optical density of the cornea at 0-2mm in the 3 months after surgery(r=-0.219,P=0.024;r=-0.235,P=0.017;r=-0.210,P=0.033).It was also negative correlated with the corneal densitometry in the 0-2mm area 3 months after surgery(r=-0.234,P=0.029),and was significantly positively correlated with the corneal densitometry in the 0-2mm area 6 months after surgery(r=-0.438,P=0.007).There was no significant correlation between the thickness of the remaining matrix bed and the overall corneal densitometry at each postsurgical period.7.Sh gradually increased from 1 week postsurgically to 6 months postsurgically,and there was a statistically significant difference between each time period(P<0.001);C40 gradually increased from postsurgical 1 week to postsurgical 6 months postsurgically.The difference was statistically significant at 3 months and 6 months after surgery(P=0.007),but there was no significant difference between 1 month and 6 months postsurgically;C31 postsurgically 1 to postsurgical 3 Month gradually increased,C3-1 decreased at 6 months postsurgically compared with 3 months postsurgically,C3-1 had statistically significant difference at each time period compared with presurgical(P<0.001),C31 at postsurgical 3 months The difference was statistically significant before surgery;C3"3 gradually increased from 1 week postsurgically to 1 postsurgical month,declined to presurgical level 3 months postsurgically and stabilized to 6 months postsurgically,but postsurgically There was no statistically significant difference before surgery(P=0.305).C33 was lower than presurgical level at 1 week postsurgically,and it gradually increased after 1 month after surgery,but the difference between postsurgical time and presurgical comparison was not significant.(P=0.752).8.There was a significant negative correlation between presurgical SE and postsurgical Sh.(r=-0.460,P<0.001;r=-0.411,P<0.001;r=-0.439,P<0.001;r=-0.378,P =0.019),There was a significant negative correlation between the presurgical SE and the C40 at 1 week postsurgically and 3 months postsurgically(r=-0.198,P=0.038;r=-0.233,P=0.014;r=-0.375,P<0.001).There was a negative correlation between presurgical cylinder and C40 from 1 week to 3 months postsurgically(r=-0.220,P=0.021;r=-0.392,P=0.006;r=-0.344,P=0.001).There was a positive correlation between SE and C3-1 at 1 week and 1 month after surgery(r=0.190,P=0.047;r=0.215,P=0.028),and there was negative between presurgical SE and C3"3 from 1 week postsurgically to 3 months postsurgically.(r=-0.227,P=0.017;r=-0.266,P=0.006;r=-0.274,P=0.011);However,there was no correlations between presurgical SE and postsurgical C3-1,C31,C3-3,C33.And there was also no correlation between presurgical cylinder and postsurgical Sh,C31,and C33(P>0.05).9.There was a significant positive correlation between the central lens thickness and the Sh at each postsurgical period(r=0.321,P=0.001;r=0.406,P<0.001;r=0.361,P=0.001;r=0.0389,P=0.016).There was a significant positive correlation between SE and C40 1 week and 3 month after surgery.(r=0.452,P<0.001;r=0.236,P=0.006;r=0.224,P=0.041).There was no correlation between the central lens thickness and the postsurgical C3-1,C31,C3-3,and C33(P>0.05).There was a negative correlation between RST and postsurgical Sh(r=-0.403,P<0.001;r=-0.339,P<0.001;r=-0.251,P=0.021;r=-0.411,P=0.010).10.The total corneal densitometry was only slightly positively correlated with corneal Sh at 1 month after surgery(r=0.200,P=0041).It was slightly positively correlated with the corneal densitometry and Sh of the 6-10mm region at 1 week,3month,6month after surgery.There was a negative correlation between corneal total Sh at the 1st week,3 months postsurgically,and 6 months postsurgically(r=-0.216,P=0.025;r=-0.242,P=0.028;r=-0.419,P= 0.011).The corneal densitometry of other layer and region only correlate with Sh of the cornea after SMILE surgical for onetime,such as C3-1,C31,C3-3,C33,C40,etc.The correlation was not significant between other factors and Sh(P>0.05).Conclusion1.The early corneal densitometry value in the surgical area after SMILE will transiently increase but the corneal densitometry gradually recovers to the presurgical level with time.This proves that corneal densitometry can be used as an objective monitoring index of postsurgical corneal transparency.2.The corneal densitometry and high-order aberrations afterare related to the central thickness of the cornea lens.Surgeons should pay attention to the postsurgical corneal densitometry and higher-order aberrations when performing SMILE surgery on patients with higher refractive power.3.The corneal high-order aberrations of Sh,C40,C3-1,and C31 after SMILE were higher than that before surgery,but they gradually became stable with time.Therefore,the visual quality of SMILE was stable after SMILE.4.There was no significant correlation between the corneal densitometry and corneal high-order aberrations after SMILE.Therefore,the corneal opacity decrease in the early postsurgical period had no significant effect on the high-order aberrations of the cornea. |
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