Effects of a high level of illumination before sleep at night on chorioretinal thickness and ocular biometry
Introduction
As industry expands and economies grow, the nocturnal exposure to bright light increases. If this unnecessary nocturnal light causes human or ecosystem damage, it is considered light pollution (Longcore and Rich, 2004). People in developed nations are exposed to bright light at nighttime before sleep through smartphone, computer, and television. Many studies have evaluated changes in the human body that result from abnormal or unnatural light exposure because of an increasing interest in light pollution(Fonken et al., 2010, Kloog et al., 2010, Obayashi et al., 2013, Obayashi et al., 2015, Parent et al., 2012). Bright light at night has been reported to promote depression, carotid atherosclerosis, obesity, diabetes mellitus, and cancer via disruption of the biological clock through photosensitive retinal ganglion cells, a non-visual photoreceptors. Non-visual photoreceptors include chromatophores, the aboral surface of the sea urchin, and the intracellular eye of warnowiid dinoflagellates (Cronin and Johnsen, 2016). The eye is the primary organ for sensing light, but most studies of the effects of light exposure have been confined to endocrinology and psychiatry; studies of structural changes in the human eye with evening light exposure have been insufficient.
There have been numerous animal studies regarding the effects of light on ocular refraction. When raised in a normal visual environment, under normal light intensity with a normal circadian light/dark cycle, animal species have typically been observed to develop emmetropia or low levels of hyperopia (Feldkaemper et al., 1999, Gottlieb et al., 1987, Li et al., 2000, Stone et al., 2013, Wallman and Adams, 1987). Under low light intensity and a normal circadian light/dark cycle or darkness, refractive error tends to be myopic (Cohen et al., 2011, Feldkaemper et al., 1999, Norton et al., 2006). Under continuous normal illuminance or bright light and a normal circadian light/dark cycle, refractive error tends to be hyperopic (Cohen et al., 2011, Lauber, 1987, Li et al., 2000). There have been few human studies about the effects of light on the eye; one revealed that greater daily light exposure was associated with slower axial eye growth in childhood (Read et al., 2015).
The choroid is a highly vascularized tissue that provides oxygen and nourishment to the outer retinal layer (Hayreh, 1975, Hayreh, 1990). Recent studies have suggested that the choroid is involved in various vision-threatening diseases, including degenerative myopia and age-related macular degeneration (Oh et al., 2014). With the development of imaging technologies, it has become possible to observe changes in the microstructure of the eye. In particular, optical coherence tomography (OCT) can be used to directly measure changes in the retina and choroid. Choroidal thickness is affected by age, refractive error, and axial length (Ikuno et al., 2010, Tuncer et al., 2015). Many factors, including smoking, physical exertion, and consumption of water or alcohol, can cause short-term changes in choroidal thickness (Kang et al., 2016, Mansouri et al., 2013, Sayin et al., 2015, Sizmaz et al., 2013). Previous studies have also reported diurnal variation in choroidal thickness (Brown et al., 2009, Chakraborty et al., 2011, Lee et al., 2014, Nickla, 2013, Nickla et al., 2002, Tan et al., 2012, Usui et al., 2012). In addition, changes in illumination have been suggested to influence choroidal blood flow and thickness (Alagoz et al., 2016, Fuchsjager-Mayrl et al., 2001, Lan et al., 2013, Longo et al., 2000, Nickla and Totonelly, 2016). However, the effects of bright light before sleep at night on the human eye are not well established.
In the current study, we investigated the influence of bright light before sleep at night on eye structures in healthy adults.
Section snippets
Methods
The Institutional Review Board of Korea University Medical Center approved this study, and all research and data collection were conducted in accordance with the tenets of the Declaration of Helsinki. Informed consent was obtained from all study participants. Prior to enrollment, each participant's best-corrected visual acuity was measured with a Snellen chart, and intraocular pressure was measured by non-contact tonometry (CT-80A, Topcon Co., Tokyo, Japan). An alternate cover test at far and
General characteristics of participants
Table 1 summarizes the baseline characteristics of the 27 participants with 12 right eyes and 15 left eyes. There was no difference between right and left eyes except mean keratometry. The inter-observer correlation value for photoreceptor layer thickness and subfoveal choroidal thickness measurements was 0.846 (95% confidence interval, 0.821–0.869) and 0.894 (95% confidence interval, 0.876–0.910). Bland-Altman plots revealed that photoreceptor layer thickness and subfoveal choroidal thickness
Discussion
The baseline characteristics of this study revealed that central macular thickness, macular volume and subfoveal choroidal thickness are related to refractive error and axial length. These findings are similar to those of previous studies (Harb et al., 2015, Luo et al., 2006, Othman et al., 2012, Tuncer et al., 2015, Zhao et al., 2016). While subfoveal choroidal thickness was related to age in earlier studies, the relationship between subfoveal choroidal thickness and age was not significant in
Conclusions
Bright light exposure before sleep at an intensity as high as 1000 lux induced an in-phase shift in amplitude of choroidal thickness. Diurnal variation in choroidal thickness can be affected by bright light exposure before sleep.
Funding
This study is supported by the Korean Ministry of Environment through “The Environmental Health Action Program (2012001350010)” and a grant from Korea University College of Medicine (K1600851).
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