Chromatic Aberration Measurement Technology In Human Eye

Optic errors of the human eye are divided into monochromatic and chromatic aberrations.Hartmann wavefront sensing technique and adaptive optics technology make monochromatic aberration well measured and corrected.These techniques have been widely used in high-resolution retinal imaging and vision studies.After the monochromatic aberration corrected,the chromatic aberration of human eye has become the main factor that affects the resolution of multi-wavelength fundus imaging and the visual performance of intraocular lens.It is of great value to evaluate the chromatic aberrations of human eye in real timefor improving the accuracy of multi-wavelength fundus imaging and the visual performance of intraocular lens.Nowadays,the method of objectively evaluating human eye chromatic aberration based on adaptive optics technology has been published,in which the measurement of longitudinal chromatic aberration has achieved clinical application.However,the current study of chromatic aberration only focuses on only longitudinal chromatic aberration(or axial chromatic aberration,LCA)or transverse chromatic aberration(or lateral chromatic aberration,TCA);most of methods are time-sharing measurements without considering the influence of eye movement.In addition,whether the double-pass system,which is employed to measure monochromatic aberration,can be well applied to the measurement of human eye chromatic aberration needs further study.Therefore,it is of great significance to realize the objective and simultaneous measurement of two kinds of human eye chromatic aberration.In this background,combined with the achievements of previous research,this paper mainly carried out the following work:(1)To study whether double-pass system is able for the measurement of human eye chromatic aberration.TCA is obtained by the odd aberration of different wavelengths,but in the early research,the odd aberration in the two passes had cancellation;so it is necessary to re-study the principle of the double-pass system.In this paper,a new model eye is developed to verify whether the double-pass system is able to measure the odd aberration.A typical human eye double-pass system-Hartmann wavefront aberration measurement system was developed to measure the typical odd aberration-coma.The experiment showed that in the double-pass system,the odd aberration of human eye could be measured whenthe entrance pupil and exit pupilsize were equal.Human eye's odd aberration was not related to the size of entrance pupil and exit pupil.Besides,double-pass system did not cancel human eye's odd aberration.The results show that the human eye double-pass system is suitable for the study of human eye chromatic aberration.(2)The principle experiment of human eye chromatic aberration measurement.A system for simultaneous measurement of LCA and TCA in human eyes was developed.Two Hartmann wavefront sensors were developed to simultaneously measure wavefront of two wavelengths.First,the chromatic aberration between red light(639nm)and infrared light(786nm),green light(532nm)and infrared light(786nm)in model eye was measured respectively.The chromatic wavefronts were converted into Zernike polynomials.The Zernike tilt coefficient(first-term)was used to calculate TCA along the x-direction,while the Zernike defocus coefficient(forth-term)was used to calculate LCA.In the model eye experiment,TCA changed linearly with the displacement of the measurement position of the model eye.However,the variation of TCA with wavelength was not linear,and TCA change with eccentricity in the short spectral range was faster than the long spectral range.In addition,human eye chromatic aberration in central field of view was measured;the average value of LCA was 0.34 D,the horizontal TCA was 2.496 arcmin,and the vertical TCA was 0.458 arcmin.The individual difference of LCA was insignificant.However,TCA significantly varied among the subjects,even between the eyes of the same subject.Finally,the results of chromatic aberration measurement were compared with previous studies,which verified the feasibility of the chromatic aberration measurement method proposed in this paper.(3)Chromatic aberration measurement based on adaptive optics technology across the visual field.Considering the influence of monochromatic aberration,the Badal focusing technology and adaptive optics technology were introduced to correct monochromatic aberration together.In the case of monochromatic aberration correction,the residual aberration RMS was less than 0.29?m.TCA of human eye was obtained by deviation of point-spread function(PSF)images and LCA was calculated from Zernike defocus across-10° to 10°field of view.The change of TCA with eccentricity was 0.162 arcmin/degree.Compared with the previous studies,TCA was not linear with the change of wavelengths.It further showed that the change of TCA with eccentricity was faster in the short band than that in the long band.LCA increased or decreased with the change of the view field.Near the eye axis(5° in temporal side),LCA was the smallest;the average LCA value was 0.37 D.LCA increases with the eye axis deviates from the measuring axis.(4)To evaluate the measurement error of human eye chromatic aberration measurement system.The error sources of PSF collection in fundus camera and wavefront collection in Hartman wavefront sensor were analyzed.The accuracy and repeatability of human eye chromatic aberration measurement system was evaluated.