Customized Human Eye Modelling And Precision Corneal Refractive Surgery

Human eye is a complex and delicate optical imaging system,casting the colorful world onto the retina.However not all the eyes are emmetropic,according to incomplete statistics,there are 20-30% population across the global suffered from ametropia,including myopia,hyperopia,astigmatism,the combination and etc.Among them,myopia is majority and thus regarded as one of three-most-significant diseases of mankind.The corneal refractive surgery mainly aims to correct the myopic“defocus” errors to improve the vision acuity of the eye through removing appropriate amount of corneal stroma to flatten its anterior surface.The laser refractive surgery has been developing decades into multiple surgical schemes in clinical trials,however the performances and results are diversified.In the mean-time,the eye is an imperfect imaging system with compound structures possessing intrinsic optical aberrations,thus its ultimate spatial resolution is worse than the diffraction limit of an aberration-free aperture in equal-size.The eye-ball is not a perfect sphere either,the inhomogeneous refractive distributions and irregularities across the boundaries of its various internal media prevent the conventional surgery schemes from precise compensation of the optical errors.Especially there are reports that many patients are still disturbed by the post-surgery side-effects e.g.halo?ghost?dizziness etc.at dusk or night even after a successful laser-eye surgery.So we developed personalized eye models and simulated surgery schemes in order to resolve the problems of vision loss and imaging distortion at relatively dim environment,and to gain the optimal rectification of the optical aberrations for the eye.In this dissertation,we established a customized eye-model for the reprentative myopia at-2D or-5D,concerning of the intra-ocular “astigmatism” and intrinsic high-order aberrations associated with the inhomogeneous or irregular refractive distributions in the bulk of the eye in the meantime.Then we systematically investigated and assessed the post-surgery vision quality for three typical schemes: i)spherical,ii)optimized-Q,and iii)wave-front guided,by utilizing the advanced techniques in modern optometry: a)spot diagram at the fovea,b)the overall wave-front aberrations of the eye-ball,and c)modulation transfer function.Moreover,the “astigmatism” reflects the asymmetric refractive distributions of the eye,and is one of the most fundamental optical aberrations besides the defocus.Since the conventional corneal refractive surgery rectifies the eye's optical aberration through modifying the profile of cornea anterior,does not really concern the origin of astigmatism.Then we parametrized a personalized-5D myopic model with two types of astigmatism: corneal astigmatism and intra-ocular astigmatism simulated and evaluated the results before or after three aforementioned surgery schemes(spherical,optimized-Q,and wave-front guided).The results show: i)spherical or Q correction scheme could reduce corneal astigmatism,however the rectification to intra-ocular astigmatism is poor;ii)spherical scheme would introduce substantial “spherical aberration”,which could be well restricted by the optimized-Q scheme,but neither of them is able to correct other types of high-order aberrations;iii)among all three,thewave-front guided Lasik could correct various types of optical aberrations either in low or high orders in general to deliver the best retina imaging,or even super vision.