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Review
. 2008 Nov;92(11):1439-44.
doi: 10.1136/bjo.2008.141747. Epub 2008 Aug 29.

Circadian Photoreception: Ageing and the Eye's Important Role in Systemic Health

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Free PMC article
Review

Circadian Photoreception: Ageing and the Eye's Important Role in Systemic Health

P L Turner et al. Br J Ophthalmol. .
Free PMC article

Abstract

Aim: To analyse how age-related losses in crystalline lens transmittance and pupillary area affect circadian photoreception and compare the circadian performance of phakic and pseudophakic individuals of the same age.

Methods: The spectral sensitivity of circadian photoreception peaks in the blue part of the spectrum at approximately 460 nm. Photosensitive retinal ganglion cells send unconscious information about environmental illumination to non-visual brain centres including the human body's master biological clock in the suprachiasmatic nuclei. This information permits human physiology to be optimised and aligned with geophysical day-night cycles using neural and hormonal messengers including melatonin. Age-related transmittance spectra of crystalline lenses and photopic pupil diameter are used with the spectral sensitivity of melatonin suppression and the transmittance spectra of intraocular lenses (IOLs) to analyse how ageing and IOL chromophores affect circadian photoreception.

Results: Ageing increases crystalline lens light absorption and decreases pupil area resulting in progressive loss of circadian photoreception. A 10-year-old child has circadian photoreception 10-fold greater than a 95-year-old phakic adult. A 45-year-old adult retains only half the circadian photoreception of early youth. Pseudophakia improves circadian photoreception at all ages, particularly with UV-only blocking IOLs which transmit blue wavelengths optimal for non-visual photoreception.

Conclusions: Non-visual retinal ganglion photoreceptor responses to bright, properly timed light exposures help assure effective circadian photoentrainment and optimal diurnal physiological processes. Circadian photoreception can persist in visually blind individuals if retinal ganglion cell photoreceptors and their suprachiasmatic connections are intact. Retinal illumination decreases with ageing due to pupillary miosis and reduced crystalline lens light transmission especially of short wavelengths. Inadequate environmental light and/or ganglion photoreception can cause circadian disruption, increasing the risk of insomnia, depression, numerous systemic disorders and possibly early mortality. Artificial lighting is dimmer and less blue-weighted than natural daylight, contributing to age-related losses in unconscious circadian photoreception. Optimal intraocular lens design should consider the spectral requirements of both conscious and unconscious retinal photoreception.

Conflict of interest statement

Competing interests: PLT has received travel grants from Advanced Medical Optics, Incorporated. MAM serves as a consultant for Advanced Medical Optics, Iridex and Ocular Instruments Corporations.

Figures

Figure 1
Figure 1. Spectral sensitivity of photopic, scotopic and circadian (melatonin suppression) photoreception. Peak sensitivities of circadian, scotopic and photopic photoreception are 460 nm (blue), 506 nm (green) and 555 nm (green-yellow), respectively. Spectral absorptance is shown for 30D blue blocking (AcrySof SN60AT, Alcon Laboratories, Fort Worth, TX) and UV-only blocking (ClariFlex, Advanced Medical Optics, Santa Ana, CA) intraocular lenses (IOLs). The area between the two IOL curves is the violet, blue and green light blocked in comparison with a UV-only blocking IOL.
Figure 2
Figure 2. Light levels in contemporary and natural environments and also in phototherapy for seasonal affective disorder, which is typically 2500 lux for 2 h/day or 10 000 lux for 30 min/day. Illuminances are given in units of photopic lux. Photopic lux accurately describe the effectiveness of a particular light exposure for overall cone photoreception, which has a peak sensitivity at 555 nm in the green–yellow part of the spectrum (cf, fig 1). A standard circadian lux unit is needed but has not been adopted yet for comparing the effectiveness of different light exposures for circadian photoreception, which has peak sensitivity at 460 nm in the blue part of the spectrum (cf, fig 1).
Figure 3
Figure 3. Age-related losses in retinal illumination due to decreasing crystalline lens light transmission and pupil area. Percentage losses per decade are reasonably uniform and most prominent at shorter violet (400–440 nm) and blue (440–500 nm) wavelengths.
Figure 4
Figure 4. Age-related losses or gains in circadian photoreception relative to a 10-year-old eye for phakic eyes, for 20 and 30D blue-blocking (AcrySof SN60AT, Alcon Laboratories, Fort Worth, TX) and for UV-only blocking intraocular lenses (IOLs) regardless of dioptric power (ClariFlex, Advanced Medical Optics, Santa Ana, CA). Cataract extraction with IOL implantation produces significant gains over phakic eyes, particularly with UV-only blocking IOLs that do not filter out shorter wavelengths vital for non-visual photoreception.

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