There is no doubt that time takes its toll on our eyes, and now a funky, Hitchcockian video of 64 eyeballs, all rolling and blinking in different directions, is providing a novel visual of one way in which this happens.
While pupils remain sensitive to changing light conditions, pupil size can decrease up to about 0.4 millimetres per decade, researchers wrote in Royal Society Open Science.
“We see a big age effect,” Manuel Spitschan, a neuroscientist at Max Planck Institute for Biological Cybernetics in Tubingen, Germany told Science News.
The change helps explain why it can be increasingly harder for people to see in dim light as they age. Light travels through the dark pupil in the centre of the eye to the retina, the layer of cells in the back of the eyes that converts the light into images.
The pupil’s size can vary from 2mm to 8mm in diameter, depending on light conditions, getting smaller in bright light and larger in dim light.
“With a small pupil, less light enters the eye,” Spitschan says.
In the lab, researchers can isolate specific aspects of light, such as intensity or wavelength, as they measure the pupil’s response.
But it’s important to understand this natural physiological phenomenon in the real world, too, Spitschan says.
That’s why the team rigged 83 volunteers, ages 18 to 87, with futuristic-looking headgear that captured data on light wavelengths and eye movements as study participants spent time walking outdoors, inside under artificial light and working at computers.
The video compilation of 64 participants’ eyes “lets you really appreciate that there are significant differences in pupil size between individuals”, he adds.
The team believes this type of work could one day contribute to the development of tailored, more efficient visual and lighting solutions for older people.
Study details
Regulation of pupil size in natural vision across the human lifespan
Rafael Lazar, Josefine Degen, Ann-Sophie Fiechter, Aurora Monticelli, and Manuel Spitschan.
Published in Royal Society Open Science on 19 June 2024
Abstract
Vision is mediated by light passing through the pupil, which changes in diameter from approximately 2mm to 8mm between bright and dark illumination. With age, mean pupil size declines. In laboratory experiments, factors affecting pupil size can be experimentally controlled. How the pupil reflects the change in retinal input from the visual environment under natural viewing conditions is unclear. We address this question in a field experiment (N = 83, 43 female, 18–87 years) using a custom-made wearable video-based eye tracker with a spectroradiometer measuring near-corneal spectral irradiance. Participants moved in and between indoor and outdoor environments varying in spectrum and engaged in a range of everyday tasks. Our data confirm that light-adapted pupil size is determined by light level, with a better model fit of melanopic over photopic units, and that it decreased with increasing age, yielding steeper slopes at lower light levels. We found no indication that sex, iris colour or reported caffeine consumption affects pupil size. Our exploratory results point to a role of photoreceptor integration in controlling steady-state pupil size. The data provide evidence for considering age in personalised lighting solutions and against the use of photopic illuminance alone to assess the impact of real-world lighting conditions.
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