J Vis. 2023 Dec 1;23(15):76. doi: 10.1167/jov.23.15.76.
As humans look around the environment, the crystalline lens inside the eye changes optical power to bring retinal images into focus. This visuomotor response is called accommodation. For a given accommodative state, light at only one wavelength can be in focus because the eye contains significant chromatic aberration. We examined how the visual system weights different wavelengths for focusing polychromatic stimuli, especially those with peaks at more than one wavelength. With an autorefractor, we continuously measured human accommodative responses (at 30 Hz) to stimuli comprising various mixtures of short- and long-wavelength content. In a series of trials, seven human observers viewed a three-letter word stimulus spanning 1.5° (24 arcmins per letter) against a black background on an AMOLED display for seven seconds. The optical distance of the screen was varied using a focus-adjustable lens. Halfway through the trial, the stimulus underwent a step change in optical distance (±0.75, 1.00, or 1.50 diopters). Simultaneously, the color of the stimulus changed. Accommodative responses for each subject were analyzed with nested descriptive models, including a color-free model, a weighted-averaging model, and a color-switching model. The results show that stimulus color significantly influences the dynamic accommodative response, and that long wavelengths influence the response more than short wavelengths, even when their luminance is the same.