Effects Of Adaptive Optics Correction Of Ocular Aberrations On Binocular Summation

Human being has binocular vision and uses it to perceive the three-dimensionalworld. Binocular vision does not integrate the information from the two eyes linearly.Compared with monocular vision, binocular vision provides many critical advantages.For instance, binocular stereopsis greatly improves the ability to code depth.Additionally, visual performance on a detection or discrimination task is usually betterwith two eyes open, which terms “binocular summation”. The studies on binocularvision show important values on various research fields such as visual neural processing,diagnosis and therapy of amblyopia, three-dimensional display and so on.Adaptive optics (AO) techniques allow dynamically correcting the ocularaberrations to achieve a diffraction-limited retina image. By testing visual function withand without correction of ocular aberrations, one can analyze the impact of these ocularaberrations on the visual function. Adaptive optics has been intensively applied invision research. However, a typical AO visual system is usually designed for monocularvision, which is not suitable for the binocular vision research. Thus, a natural step inthis field is to design a binocular adaptive optics visual system (BAOVS).In this thesis, firstly, the feature and importance of binocular vision is introduced,the necessity to develop a BAOVS is discussed and the research progress in related fieldis reviewed. Secondly, some basic concepts and knowledge on visual physiology, ocularoptics, adaptive optics and visual psychophysics are given. Thirdly, the design andvalidation of the BAOVS are presented, and next the effects of ocular aberrations onbinocular summation are elucidated through three aspects, i.e. light level, binoculardisparity and background noise.(1) System design, calibration and experimental test of the binocular adaptiveoptics visual simulator are presented. First, the measurements of binocular aberrations,dual-AO system control and the visual stimulus device are described, and the systemdesign parameters are given. Secondly, the performance of the system is calibrated,including the laser exposure safty for the human eyes, the accuracy of the measurementof the binocular aberrations and the correction capability for the dual-AO system.Thirdly, the parallelism of the binocular optical axis and the linearity of the visualdisplay are carefully calibrated. Finally, the first experimental test is given. (2) Effects of ocular aberrations on binocular contrast detection in different spatialfrequencies and light levels are studied. For all conditions, AO correction of ocularaberrations improves the binocular/monocular contrast sensitivity significantly. For bothlight levels (1and100cd/m2), the binocular AO benefits in contrast sensitivity show nosignificant difference with the benefit achieved monocularly. For signal at8and16cpd,the visual benefit increase with the increase of light level. For all tested signal at threespatial frequencies (2,8and16cpd), binocular summations are similar for conditionswith and without AO correction of ocular aberrations at high light level. For low lightlevel, binocular summation slightly decreases with AO correction.(3) Effects of ocular aberrations on binocular contrast detection in different spatialfrequencies and binocular disparities are investigated. The binocular contrast thresholdincreases as the disparity increasing. For signal spatial frequency of4cpd, the binocularthreshold shows a systematical drop with AO correction of the ocular aberrations. For8cpd signal, the magnitude of binocular threshold drop due to AO correction increasewith increasing binocular disparity. A nonlinear model is developed to fit the data andthe results could be explained by the nonlinear mechanism in binocular summationwhich is related to both the disparity and the signal contrast.(4) Effects of ocular aberrations on contrast detection in various levels ofwhite-noise background are studied. The experiments are performed both monocularlyand binocularly, and the effects of ocular aberrations on binocular summation are alsogiven. The results show that ocular aberrations always harm contrast detection in weaklevels of noise, whereas they could be beneficial for contrast detection in high levels ofnoise. The implications of these finds are discussed in frame of linear amplifier modeland contrast gain control mechanism. For high levels of noise, if ocular aberrationsproduce more degradation to the noise masking than to the signal, they will benefit thedetection. The degradation of noise masking due to ocular aberrations can be from twopossible sources:(1) reduction of the random variations or (2) relief from thecross-channel suppression. Furthermore, the ocular aberrations moderate thedegradation of binocular summation in high level of noise.