ABSTRACT
@#AIM: To compare the difference between the actual cutting amount and the preoperative predicted amount of corneal stroma after the small incision lenticule extraction(SMILE), and evaluate the predictability and accuracy of SMILE for corneal stroma. <p>METHODS: Prospective study. A total of 113 myopic patients(220 eyes)who had taken SMILE in the Affiliated Hospital of Yunnan University were selected, and routine examinations were carried out before and 1,3mo after operation, including visual acuity, non-contact tonometer(NCT), spherical equivalents(SE), mean corneal curvature, spherical coefficient of anterior corneal surface and Pentacam anterior segment analysis. All the 102 eyes in the research objects were randomly selected to measure the central corneal thickness(CCT)with the A-supersonic cornea thickness gauge before and 3mo after operation. The actual cutting amount after operation is the difference between the thickness of the thinnest spot of the cornea before and after operation, and the error amount is the difference between the predicted cutting amount before operation and the actual cutting amount after operation. The cutting error amount was observed and its correlation with physiological parameters before operation was analyzed. <p>RESULTS: SMILE had a good performance and the corneal morphology and visual acuity were relatively stable 1 and 3mo after operation. The consistency was good between the data measured by the A-supersonic cornea thickness gauge and the data of the thinnest spot of the cornea in the Pentacam anterior segment analysis, where the difference had no statistical significance(<i>t</i>= -1.877, <i>P</i>=0.063). The difference between the predicted cutting amount before operation(101.36±18.91)μm, and the actual cutting amount 1mo after operation(88.89±18.69)μm and 3mo after operation(84.95±18.64)μm(<i>F</i>=334.65, <i>P</i><0.01)had statistical significance; There was statistical difference between the cutting amount 1 and 3mo after operation, and the predicted errors before operation \〖(12.59±9.78)μm and(16.50±9.21)μm\〗. The cutting amount errors were only correlated with the preoperative equivalent diopter(<i>r</i>=0.299, <i>P</i><0.01)and(<i>r</i>=0.305, <i>P</i><0.01). The equivalent diopter at 1 and 3mo after operation was correlated with the cutting amount error at the same time(<i>r</i>=-0.275, <i>P</i><0.01)(<i>r</i>= -0.306, <i>P</i><0.01). With the increase of the cutting amount error, the postoperative spherical equivalent shifted to negative.<p>CONCLUSION: The actual cutting amount of corneal stroma after SMILE is smaller than the predicted preoperative cutting amount, and the predicted cutting amount error increases with the increase of preoperative diopter. As the cutting amount error increases, postoperative diopter gradually shifted to negative. The error, however, does not influence the target's visual acuity in the early postoperative period.
ABSTRACT
@#AIM: To explore the correlation between corneal biomechanics and corneal densitometry.<p>METHODS: Prospective study. Patients who examined before corneal refractive surgery in the Second People's Hospital of Yunnan Province from March 2019 to June 2019 were selected as research objects. Pentacam HR system was used to evaluate corneal densitometry. The corneal was divided into three areas around the corneal apex with diameters of 0-2mm, >2-6mm, >6-10mm,and the corneal thickness was divided into anterior, middle and posterior layers. The thinnest point thickness of cornea in Pentacam HR was selected to be included in the study. Corvis ST was used to measure the biomechanical parameters, including the first applanation length(AP1L)and applanation velocity(AP1V),the second applanation length(AP2L)and applanation velocity(AP2V),the highest concavity peak distance(PD),highest concavity radius(HCR)and deformation amplitude(DA). Pentacam & Corvis ST comprehensive diagnostic platform software was used to comprehensively analyze the examination results and obtain comprehensive corneal biomechanical parameters(CBI), as well as other independent parameters including stiffness parameters(SP), integrated radius(IR), Ambrosio relational thickness-horizontal(ARTh)and deformation amplitude ratio(DAR). Variance analysis was used for the difference of corneal densitometry in each region, the correlation between corneal biomechanical parameters and corneal densitometry was analyzed by Pearson or Spearman.<p>RESULTS: The difference of optical density between different diameter ranges and different layers was statistically significant(<i>F</i>=35.101, <i>P</i><0.01; <i>F</i>=1002.897, <i>P</i><0.01), CBI was correlated with AP2L,AP2V,PD,DA,SP,IR,ARTh and DAR in the independent biomechanical parameters(<i>r</i>s= -0.502, <i>P</i><0.01; <i>r</i>s=-0.457, <i>P</i>=0.001; <i>r</i>s=0.428, <i>P</i>=0.002; <i>r</i>s=0.539, <i>P</i><0.01; <i>r</i>s=-0.687, <i>P</i><0.01; <i>r</i>s=0.716, <i>P</i><0.01; <i>r</i>s=-0.728, <i>P</i><0.01; <i>r</i>s=0.750, <i>P</i><0.01). CBI was positively correlated with optical density within the range of 0-2mm(<i>r</i>=0.343, <i>P</i>=0.015). The corneal densitometry within a range of 0-2mm is correlated with AP2L, IR, ARTH and DAR in independent biomechanical parameters(<i>r</i>s=-0.298, <i>P</i>=0.035; <i>r</i>s=0.368, <i>P</i>=0.009; <i>r</i>s=-0.419,<i> P</i>=0.002; <i>r</i>s=0.493, <i>P</i><0.01).<p>CONCLUSION: There is a correlation between corneal biomechanics and corneal densitometry in the central region of cornea, which has a more significant correlation with the biomechanics.