The Keratectasia Volume(KEV)in Corneal Topography To Evaluate The Effect Of Corneal Collagen Cross-Linking In Pediatric Keratoconus

BackgroundKeratoconus(KC)is described as progressive corneal disease caused by non-inflammatory lesions of corneal stroma collagen.The main features are corneal thinning,asymmetric degeneration,and anterior conical protrusion in both eyes.Compared with keratoconus in adults,the illness can be more advanced and serious in adolescent patients.The current main treatment methods are wearing frame glasses,corneal rigid contact lens correction,corneal collagen cross-linking surgery(CXL),corneal stroma ring implantation,penetrating keratoplasty,deep lamellar keratoplasty(Deep Anterior Lamellar Keratoplasty,DALK).And CXL has been widely applied in the adult patients and has confirmed curative effects.While in adolescent patients,the rate of postoperative ectasia progression is higher than that of adults.The setting of ultraviolet energy is still in the exploratory stage,and accurate and reliable parameters are needed to be modified in the evaluation of corneal ectasia.At present,there is no clear and consistent understanding of the indicators for monitoring the progress of corneal ectasia.The curvature value parameter Kmax of corneal topography and the thinnest thickness of the cornea are mainly used for evaluation,but Kmax is only a single curvature value parameter from topography map.In some patients with corneal ectasia progression,the Kmax remains stable and even decrease,which limit the evaluation efficiency;the correlation between the thinnest corneal thickness and corneal ectasia is lower than the Kmax value.The support vector machine(SVM)model is a two-classifier developed on the basis of statistical learning theory with good classification performance for images.Previous studies applied a diagnosis classification tree of keratoconus by extracting and identifying the characteristics of patients’ diseases,which improves the The diagnosis specificity and sensitivity of subclinical keratoconus.In this study,the support vector machine(SVM)was applied to the image recognition transformation of corneal topography.The curvature map was obtained based on the color map and the volume of the corneal protrusion was obtained.The research aims to provide new corneal ectasia evaluation parameters and to monitor the progression of corneal ectasia after corneal cross-linking,providing new ideas for the management of adolescent keratoconus.PurposeTo evaluate the keratectasia volume(KEV)before and after corneal cross-linking(CXL)in pediatric patients.MethodsThis study included 40 eyes of 25 pediatric patients(10-19 years)undergoing standard CXL.The support vector machine(SVM)algorithm was applied to transform mass pixels in corneal topography into a three-dimensioned model to calculate the KEV The KEV,Kmax,Kl,K2,Kave,keratectasia area(KEA),thinnest corneal thickness(TCT)were determined before CXL and at 3,6,12 months after surgery.The correlation between KEV and other parameters(Kmax,TCT,max decentration,eccentricity and so on)was calculated.ResultsThe KEV was 4.75±0.74 preoperatively and 4.43±1.22 postoperatively at last follow-up(p<0.002).There was strong positive correlation between the KEV and Kmax(r=0.806,p<0.0005).The preoperative KEV was 4.32±0.69 in mild to moderate keratoconus(Kmax<58D)and 5.27±0.37 in advanced keratoconus(Kmax>58D)(p<0.0005,t-test).Postoperative KEV and K readings remained stable at the early stage and the KEV showed a more drastic decreasing trend than Kmax at sixth month.Statistical significance was found in the KEV between preoperative and 6 months after surgery(p<0.0005),but not in Kmax and other parameters.In 83.3%(15 eyes out of 18 eyes)of the eyes,the preoperative KEV was greater than 4.6 in patients with significant flattening after CXL.ConclusionsCompared with K readings,the KEV can be regarded as a more sensitive index to evaluate the postoperative morphological changes after CXL in pediatric patients.