Quantitative Measurement And Imaging Of Corneal Viscoelasticity Based On Ultrasound Open System

The biomechanical properties of the cornea are of great importance to the refractive power of the whole eye,but these properties have individual difference and will be altered by a lesion or surgical operation.The early diagnosis and treatment of keratoconus,corneal ectasia,evaluation the effect of corneal collagen cross-linking treatment,preoperative surgical design and risk assessment of myopic refractive surgery,improve the effect on disease screening for glaucoma which cannot be achieved without quantitative evaluation of corneal biomechanical properties.The purpose of this study is to develop an ultrasonic system for quantitatively assessing corneal biomechanical properties in vivo.The system is built upon the basis of VerasonicsTM Vantage 256 ultrasonic open system.The system controls a linear array probe producing the acoustic radiation force to excite the cornea tissue and then using detecting the tissue vibration with the same probe.The group and phase velocity was calculated and then shear elasticity and viscosity were estimated according to lamb wave propagation model.In this study,two collagen cross-linking(CXL)treatments were designed to increase corneal stiffness,and the effects were quantitatively compared.The elasticity modulus of the group which adding 0.1% glutaraldehyde were found 148.78%?335.68%?392.59% and 250.47% in comprision with Riboflavin group under 5min,10 min,30min and 60 min UVA exposure,respectively.The estimated shear elasticity modulus were converted to Young's modulus and were compared with the results of classical tensile tests,and the result was showing that the estimated elasticity with ultrasound measurement was in agree with the results of tensile test.In addition,this study also investigates the quantitative viscoelasticity imaging of the corneal surface by burning the cornea by 4% formalin solution at two spots.The viscoelasticity imaging of the cornea were acquired before and corneal burning.The elastic imaging distinguished very well between the burned position and other positions of the cornea and the elasticity in burned region increased significantly,which show the effectiveness of the ultrasonic platform.Finally,we explore the possibility and feasibility of measuring biomechanical properties in a rabbit cornea in vivo and gain some valuable experience in living animal experiments.This study proposed a method to evaluate the corneal viscoelasticity quantitatively,evaluated its effectiveness by ex-vivo measurement of bovine corneas and demonstrated its feasibility on corneal elasticity imaging and in vivo measurement.The methods can be realized in a stand-alone system or as an additional module in commercial medical ultrasound scanning system.The method has great potential to play important roles in clinical ophthalmology in the future.