Effect of spherical aberration on the vergence-accommodation conflict.

We used a binocular adaptive optics visual simulator with vergence control to investigate the impact of spherical aberration (SA) profiles on different degrees of vergence-accommodation conflict (VAC). Stereoacuity and subjective discomfort were measured in ten subjects under three SA conditions (0, -0.24, and -0.43 µm for a 4.5-mm pupil) and three vergence disparities: -1.5 D (parallel lines of sight), 0 D, and +1.5 D (eyes converging at 33 cm), relative to a screen placed at an accommodative distance of 1.5 D. Baseline naked-eye stereoacuity was consistent with published values and showed deterioration for negative conflict (object closer than the vergence point). Adding SA did not substantially improve visual performance, possibly providing a small advantage for negative conflict but producing the opposite effect for positive conflict. No overall improvement was found in comfort level, as the subjective questionnaires revealed opposite tendencies when SA was introduced: discomfort decreased for negative VAC and increased for positive and no conflict. However, the key implication is that an intermediate amount of SA may equalize discomfort across conflict conditions, potentially reducing fatigue during prolonged viewing by avoiding peaks of visual distress. While further research is needed, this finding could have practical relevance in extended reality (ER) systems, as incorporating extended-depth-of-focus (EDoF) optics, either within the device or in the user's eye (e.g., through contact lenses), could provide a simple and cost-effective means to improve user experience.