Abstract
Purpose: :
Blue-blocking intraocular lenses have been developed for use in cataract surgery based on the theory that short wavelength visible light may damage retinal cells. A side effect of blocking blue light is a reduction in the input to melanopsin-expressing photoreceptive retinal ganglion cells (pRGCs), which have a maximal sensitivity at 480nm. These cells provide input to the circadian system and regulate the sleep-wake cycle. We know that cataract surgery improves sleep in some patients which we hypothesise to be an effect of increased blue light exposure. We looked at the transmission of different lens types and calculated their effect in the home environment to assess the likely impact of these lenses on sleep in an elderly population.
Methods: :
Lens transmission was measured in the laboratory for 3 different powers of the Acrysof SA60AT (UV-blocking) and the Acrysof Natural SN60AT (blue-blocking) lenses. The emission spectrum and intensity of three home light sources and one office light source were measured using a spectrometer. This information along with the absorption spectrum of melanopsin was used to calculate the relative reduction in light available for circadian regulation with each light source in the presence of each lens implant.
Results: :
A reduction in light available for pRGC stimulation was seen with the blue-blocker compared to UV-blocker for all light sources, varying from 11% to 22% dependent on light source.
Conclusions: :
It is likely that individuals who experience poor exposure to natural daylight do not get sufficient illumination from artificial light sources to allow robust entrainment of circadian rhythms. Those who have blue-blocking lens implants will experience further reduction in light available for absorption by melanopsin-exressing pRGCs. This may be clinically relevant in terms of sleep disruption, particularly in a population with a high prevalence of sleep problems. This will need to be addressed by improving home lighting conditions, and paying attention to the emission spectra and intensity of light sources used.
Keywords: intraocular lens • circadian rhythms • ganglion cells