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. 2017 Jul;37(4):440-450.
doi: 10.1111/opo.12385.

Attenuation of Short Wavelengths Alters Sleep and the ipRGC Pupil Response

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Free PMC article

Attenuation of Short Wavelengths Alters Sleep and the ipRGC Pupil Response

Lisa A Ostrin et al. Ophthalmic Physiol Opt. .
Free PMC article

Abstract

Purpose: Exposure to increasing amounts of artificial light during the night may contribute to the high prevalence of reported sleep dysfunction. Release of the sleep hormone melatonin is mediated by the intrinsically photosensitive retinal ganglion cells (ipRGCs). This study sought to investigate whether melatonin level and sleep quality can be modulated by decreasing night-time input to the ipRGCs.

Methods: Subjects (ages 17-42, n = 21) wore short wavelength-blocking glasses prior to bedtime for 2 weeks. The ipRGC-mediated post illumination pupil response was measured before and after the experimental period. Stimulation was presented with a ganzfeld stimulator, including one-second and five-seconds of long and short wavelength light, and the pupil was imaged with an infrared camera. Pupil diameter was measured before, during and for 60 s following stimulation, and the six-second and 30 s post illumination pupil response and area under the curve following light offset were determined. Subjects wore an actigraph device for objective measurements of activity, light exposure, and sleep. Saliva samples were collected to assess melatonin content. The Pittsburgh Sleep Quality Index (PSQI) was administered to assess subjective sleep quality.

Results: Subjects wore the blue-blocking glasses 3:57 ± 1:03 h each night. After the experimental period, the pupil showed a slower redilation phase, resulting in a significantly increased 30 s post illumination pupil response to one-second short wavelength light, and decreased area under the curve for one and five-second short wavelength light, when measured at the same time of day as baseline. Night time melatonin increased from 16.1 ± 7.5 pg mL-1 to 25.5 ± 10.7 pg mL-1 (P < 0.01). Objectively measured sleep duration increased 24 min, from 408.7 ± 44.9 to 431.5 ± 42.9 min (P < 0.001). Mean PSQI score improved from 5.6 ± 2.9 to 3.0 ± 2.2.

Conclusions: The use of short wavelength-blocking glasses at night increased subjectively measured sleep quality and objectively measured melatonin levels and sleep duration, presumably as a result of decreased night-time stimulation of ipRGCs. Alterations in the ipRGC-driven pupil response suggest a shift in circadian phase. Results suggest that minimising short wavelength light following sunset may help in regulating sleep patterns.

Keywords: actigraphy; intrinsically photosensitive retinal ganglion cells; melanopsin; melatonin; sleep.

Conflict of interest statement

Disclosure

The authors report no conflicts of interest and have no proprietary interest in any of the materials mentioned in this article.

Figures

Figure 1.
Figure 1.
(a) Flow chart of the three week experimental protocol (b) For pupillometry, subjects dark adapted for 5 min. Baseline pupil diameter was recorded for 10 s, then a 1 s long wavelength (red) stimulus was presented followed by 60 s recording, and a 5 s long wavelength stimulus was presented followed by 60 s recording. Subjects dark adapted again, and the protocol was repeated with a short wavelength (blue) stimulus.
Figure 2.
Figure 2.
Pupil diameter of the right eye during a 1 s long wavelength stimulus (red trace) presented to the left eye, overlaid with the pupil diameter during a 1 s short wavelength stimulus (blue trace) for one representative subject. ‡ indicates the maximum pupil constriction, dotted and dashed lines show where the 6 s and 30 s PIPR (post illumination pupil response) are measured, + indicates the melanopsin oscillatory responses. The area under the curve (AUC) for the blue stimulus is shaded grey, and is calculated with respect to the normalised pupil size.
Figure 3.
Figure 3.
For the baseline week, (a) night melatonin was not significantly associated with total daily log white light exposure (P = 0.32). (b) Morning melatonin levels were statistically significantly associated with total daily log white light exposure during the baseline week (P < 0.05). Circled points are outliers and not included in regression analyses.
Figure 4.
Figure 4.
Melatonin levels measured via salivary assay at night and in the morning before (solid bars) and after (open bars) wearing blue blocking glasses at night-time for 2 weeks. * indicates P < 0.05
Figure 5.
Figure 5.
Mean normalised pupil diameter for all subjects (n = 21) during a 1 s long wavelength and a 1 s short wavelength stimulus at baseline (dark red and blue, respectively) and after wearing blue blocking glasses at night-time for 2 weeks (light red and blue, respectively). 95% confidence intervals are shown in light grey for mean baseline pupil diameter and dark grey for two-week mean pupil diameter.
Figure 6.
Figure 6.
Post illumination pupil response (PIPR) metrics to 1 s and 5 s long wavelength (red) and short wavelength (blue) stimuli before (solid bars) and after (open bars) wearing blue blocking glasses at night-time for 2 weeks. (a) normalised minimum pupil diameter, (b) area under the curve (AUC), (c) 6 s PIPR, and (d) 30 s PIPR. * indicates P < 0.05.

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