Abstract
Purpose: :
Circadian rhythm is photoentrained via the retinohypothalmic tract, the initial step being stimulation of melanopsin containing retinal ganglion cells by blue light. With age, the transmission of blue light to the retina is impaired because of accumulation of chromophores in the lens of the human eye. The purpose of the study was to examine the age-induced changes in the transmission characteristics of the human lens and to study the influence of these changes on circadian rhythm and sleep.
Methods: :
Blue light transmission in the human lens and its relation to lens fluorescence were assessed in vitro in a laboratory study of 29 human donor lenses from subjects aged 1 to 78 years. This calibration enabled assessment of blue light transmission in vivo in an epidemiology study of 970 subjects aged 30 to 60 years using non-invasive ocular fluorometry. Subjects underwent a thorough physical examination. Circadian function was evaluated using questionnaire-based reports of sleeping disorders and/or national-registry based data for the subject's use of prescription sleeping medication.
Results: :
The transmission of blue light decreased by approximately 1 percentage point per year of life. Decreasing blue light transmission in the lens was associated with increased risk of insomnia or use of sleeping medication. The association remained highly significant even after correction for confounding factors such as age, sex, diabetes mellitus, cardiovascular disease and smoking.
Conclusions: :
The results demonstrated that the age-related lens yellowing significantly impairs photoentrainment of circadian rhythm probably via reduced stimulation of the melanopsin containing retinal ganglion cells. Consequently, circadian rhythm is expected to be restored when the effect of the aged lens is removed during cataract surgery.
Clinical Trial: :
http://www.clinicaltrials.gov NCT00289237
Keywords: circadian rhythms • cataract • aging