Effect Of Ocular Higher-order Aberration Correction On Stereopsis And Binocular Accommodation

The human eye’s optics has been quite intelligent after its long-term evolution.However, it is not perfect from an optical point of view and exhibits various optical aberrations. Besides the lower-order aberrations including defocus and astigmatism,the eye’s optics also has lots of higher-order aberrations that are more complex, such as coma, spherical aberration and trefoil. The existence of these higher-order aberrations not only poses a challenge on the high-resolution retinal imaging, but also degrades the visual performance. Research on the relationship of higher-order aberrations and visual performance will improve our understanding in visual optics and provide useful guidance for the optimization of visual correction strategy and for the maintenance of visual performance. However, early studies in this direction were all made under monocular vision. The normal human vision is binocular, which is not the simple summation of both eyes. Therefore, it is an inevitable trend for the study of effect of higher-order aberrations on visual performance under monocular vision to transit to that under binocular vision.In this context, this dissertation concentrates on investigating the effect of higher-order aberrations on stereopsis and binocular accommodation with a binocular adaptive optics visual simulator. Specifically, the main work of this dissertation can be summarized as follows:(1) Investigation on the effect of higher-order aberration correction on stereo threshold. The experimental results suggest that binocular higher-order aberration correction can effectively decrease stereo threshold for all subjects. Better eye higher-order aberration correction leads to a significant increase in the stereo threshold for one subject and a slight decrease for the other two subjects. The benenfit upon aberration correction is related to the exposure duration of the visual stimulus. As the duration increases, the benefit approaches the level of 1,demonstrating that the effect of the eye’s optical quality on stereopsis is weakening.(2) Investigation on the effect of higher-order aberration correction on the temporal integration property of stereopsis. The temporal integration property of stereopsis is characterized by two parameters, namely integration efficiency and time.The integration efficiency indicates the rate at which stereo threshold decreases with longer duration, and it can be quanlified by the slope of stereo threshold versusduration data in log-log coordinates; the integration time indicates the essential time for complete integration of stereopsis, and it can be quantified by the critical duration. The experimental results suggest that both the slope and the critical duration show no significant change after higher-order aberration correction,demonstrating that the temporal integration property of stereopsis is not affected by ocular aberrations.(3) Modification of the binocular adaptive optics visual simulator. To measure the accommodative response under natural vision, the system pupil needs to be adjusted from 6mm to between 4 and 5mm. This is realized through changing the matching scheme between the Hartmann wavefront sensor and the deformable mirror.First, three possible patterns of the valid subapertures in the wavefront sensor and three possible patterns of the valid actuators in the deformable mirror are proposed.Then these patterns are combined to obtain nine matching scheme of the adaptive optics system. Finally, the aberration correction capability of each scheme is analyzed using Matlab simulation, and the optimum scheme is determined as HS57-DM31 corresponding to a pupil diameter of 4.6mm. The results of actual testing show that this match scheme can achieve stable closed-loop aberration correction and the root mean square of the residual aberration is less than 0.1μm.(4) Investigation on the effect of higher-order aberration correction on the binocular accommodation. Based on the modified binocular adaptive optics visual simulator, the binocular accommodative responses are measured for stimulus levels of 0D and 1.5D, with and without binocular higher-order aberration correction, and analyzed in terms of accommodative lag, fluctuations, power spectrum density and chaos theory. The experimental results suggest no significant effect of higher-order aberration correction on accommodative lag, fluctuations and power spectrum density. Binocular higher-order aberration correction leads to a significant increase in the Lyapunov exponent for the accommodation level of 0D, whereas not for the accommodation level of 1.5D. This suggests that higher-order aberration correction is beneficial to the accommodation system, although the effect is minor under natural viewing conditions.