ABSTRACT.Purpose: 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. Methods: 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 lightinduced melatonin suppression. Results: 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. Conclusion: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.

Cataract surgery increases photoreception by the photosensitive retinal ganglion cells. Because of inconsistency between the significant findings and the many parameters that were unchanged, we can conclude that cataract surgery does not adversely affect the circadian rhythm or sleep. Longer follow-up time and fellow eye surgery may reveal the significance of the subtle changes observed. We found no difference between blue-blocking and neutral IOLs, and, because of the minor effect of surgery in itself, an effect of IOL type seems highly unlikely.

Blue-blocking IOLs increased sleep efficiency but lowered nocturnal melatonin secretion compared with neutral IOLs. Cataract surgery improved the response of ipRGCs and sleep quality. However, the effect of cataract surgery on sleep quality may be unrelated to circadian photoentrainment.