| Objective: To investigate the corneal volume(CV)and its spatial distribution in normal cornea using Pentacam HR topography;to investigate the effect of optical zone diameter on the changes of CV and corneal biomechanical properties after small incision lenticule extraction(SMILE);to investigate the variations of corneal volume(CV)after SMILE and fem tosecond laser in situ keratomileusis(FS-LASIK),and analyze the influences of biomechanical properties on the changes of CV.Methods: 1.Across-sectional study.This study included 5301 normal eyes(2911 patients).Pentacam were used to measure CV,corneal thickness(CT)and other anterior and posterior corneal parameters,utilizing pearson correlation to analyze the correlation between CV with age and corneal parameters.2.This prospective case-control study,119 eyes of 119 patients with myopia that had undergone SMILE procedure were divide into 2 groups according to optical zone(OZ): group A,OZ=6.2 mm,46 eyes of 46 patients;group B,OZ=6.5 mm,73 eyes of 73 patients.These patients were examined for corneal hysteresis(CH)and corneal resistance factor(CRF)assessed with the Ocular Response Analyzer(ORA);meanwhile,we measured CV.Pearson correlation was applied to analyze the correlation between CH and CRF and CV.Independent-samples t test was utilized to compare the parameters between the two groups.3.97 eyes of 97 patients were included in this retrospective study.CV was measured with Pentacam.CV measured within 5mm diameter was defined as central region volume(CV5),and between 5mm and 10 mm diameter was defined as peripheral region volume(CV5-10).ORA was used to assess CH and CRF.The Pearson correlation test was used to evaluate the relationship between change in CV(?CV)with change in spherical equivalence refraction(?SE),change in CH(?CH)and change in CRF(?CRF);The differences in the corneal volume between SMILE and FS-LASIK group were calculated using independent t-test;Bonferroni test was applied for multiple comparisons between different time points.Results: 1.CV and CT increase from central to paracentral area;A weak negative correlation was found between CV,CT and age,CV and CT decrease with age,however,the age-dependence of CT is stronger in paracentral area;A moderate positive correction was detected between CV and posterior curvature radius.2.The changes of corneal volume at different zone in group A were statistical significant lower than group B(all P<0.05);At postopetative 3 month,the mean reduction of CRF and CH values between two groups showed no significant difference;Positive correlations were seen between the CV values at different corneal areas and CH value or CRF value.3.CV had significant reduction after SMILE and FS-LASIK procedure(P<0.05).CV5 increased significantly from postoperative day 1 to month 3(P<0.001)in SMILE,while both CV5 and CV5-10 increased significantly in FS-LASIK(P<0.001).The increase in CV5 after SMILE was 0.11±0.16mm3,which was significantly different from FS-LASIK(0.20±0.13mm3,P=0.004).A highly positive correction was detected between the change in spherical equivalence refraction(?SE)and ?CV5 in both groups(SMILE group: r=-0.746,P<0.001;FS-LASIK group: r=-0.798,P<0.001);In SMILE group,?CV5 correlated with ?CRF(r=0.498,P< 0.001)and ?CH(r=0.374,P=0.007).In FS-LASIK group,?CV5 and ?CRF had a significant correlation(r= 0.363,P=0.012),but not with ?CH.Conclusions: 1.The CV and CT values are gradually increased from the central cornea to periphery cornea.CV and CT seems to undergo age-related reduction,expecially in peripheral area.2.The CV is associated with CH and CRF;The size of optical zone has some effects of on corneal biomechanical properties and CV after small-incision lenticule extraction,the smaller optical zone diameter has relatively less effect on the corneal biomechanical properties and CV.3.Dynamic changes in CV were found after SMILE and FS-LASIK.SMILE was associated with less change in biomechanical properties per unit of reduction in CV when compared with FS-LASIK. |
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