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Maydel Fernandez-Alonso, Abigail Finch, Gordon Love, Jenny Read; Changes in the pupillary and accommodative responses of the human eye under different illuminations. Journal of Vision 2018;18(10):583. doi: https://doi.org/10.1167/18.10.583.
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The human accommodation response has a consistent steady-state error over most of its range. For nearer distances, the response is less than required for perfect focus, and it is greater for farther distances. One hypothesis is that this results from the visual system implementing a strategy that exploits the eye's longitudinal chromatic aberration (LCA). For near targets, short-wavelength components are brought into focus, while for distant targets, long-wavelength components are in focus. To test this idea, we measured accommodation to a fixation target under monochromatic and polychromatic illumination at multiple distances. If different wavelengths are preferentially placed into focus at each distance, the response curve for monochromatic light should show a steeper slope than for polychromatic light. Dynamic measures of accommodation and pupil size were obtained from untrained observers with an infrared photorefractor. Monocular accommodation response curves were measured by changing the physical distance of the target from 0.5 to 3 diopters while keeping its angular size constant. For near targets under monochromatic light, observers accommodated appropriately to account for the changes in focus caused by LCA. However, the difference in refraction for different wavelengths progressively reduced as distance increased and by 2 metres, accommodation for all illuminations was the same. There was a significant effect of wavelength on pupil size, with smaller pupils for shorter wavelengths even when calculated luminance was equal. Accommodation to white light was comparable to that of green and orange lights at all distances, refuting the initial idea and indicating that a particular wavelength is not preferentially placed into focus in the retina as a function of distance.
Meeting abstract presented at VSS 2018
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