New research from the University of Zaragoza in Spain quantifies how the aging eye restricts the amount of circadian light reaching the retina based on photopic illuminance reaching the corneal plane and considering the optical density of an aging crystalline lens. As the researchers state:
“As a result of the described behavior, retinal illuminance may vary between individuals due to progressive age-dependent changes in the lens, causing a reduction in the amount of short-wavelength light passing through the eye and scattering [3,4,5,8,9,10,11]. Additionally, the number of intrinsically photosensitive retinal ganglion cells (ipRGCs) drops with age, changes their distribution pattern on the retina and changes their morphology [12]. Consequently, retinal photoreceptors receive less light input at older ages, particularly short-wavelength-sensitive photoreceptors (rods, S-cones and ipRGCs).”
Interestingly, it is not just the yellowing of the aging lens; there is also the reduced number and redistribution of ipRGCs with aging. As a result, a 90-year-old’s retina receives roughly 14% of the incident blue light compared to a 10-year-old’s retina. These effects help explain why the elderly stuck indoors experience significant sleep disruption.
The published research can be found here.
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