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Circadian photoreception: Aging and the eye’s important role in systemic health
  1. Patricia L. Turner (patriciaturner{at}att.net),
  2. Martin A. Mainster (martin.mainster{at}att.net)
  1. University of Kansas School of Medicine, United States
  2. University of Kansas School of Medicine, United States

    Abstract

    Purpose: To analyze 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 nonvisual brain centers including the human body’s master biological clock in the suprachiasmatic nuclei. This information permits human physiology to be optimized 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 analyze how aging and IOL chromophores affect circadian photoreception.

    Results: Aging 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 nonvisual photoreception.

    Conclusions: Nonvisual 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 aging 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.

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