Short wavelength light filtering by the natural human lens and IOLs – implications for entrainment of circadian rhythm

Abstract

Photoentrainment of circadian rhythm begins with the stimulation of melanopsin containing retinal ganglion cells that respond directly to blue light. With age, the human lens becomes a strong colour filter attenuating transmission of short wavelengths. The purpose of the study was to examine the effect the ageing human lens may have for the photoentrainment of circadian rhythm and to compare with intraocular implant lenses (IOLs) designed to block UV radiation, violet or blue light. The potential for photoentrainment of circadian rhythm was computed for 29 human donor lenses (18-76 years) and five IOLs (one UV, two violet and two blue light blocking) based on the transmission properties of the lenses and the spectral characteristics of melanopsin activation and two of it's physiological outcomes; melanopsin-driven pupillary light reponse and light-induced melatonin suppression. The potential for melanopsin stimulation and melatonin suppression was reduced by 0.6-0.7 percentage point per year of life because of yellowing of the natural lens. The computed effects were small for the IOLs and did not exceed that of a 22.2-year-old natural lens for the blue-blocking IOLs. The results show that photoentrainment of circadian rhythm may be significantly impaired in older subjects because of the colour filtering characteristics of the human lens, whereas the effects were small for all three types of IOLs studied. Consequently, the ageing process of the natural lens is expected to influence the photoentrainment of circadian rhythm, whereas IOLs are not expected to be detrimental to circadian rhythm.