Daily and Seasonal Variation in the Spectral Composition of Light Exposure in Humans

Open-Source Python Module for the Analysis of Personalized Light Exposure Data from Wearable Light Loggers and Dosimeters

Light exposure fundamentally influences human physiology and behavior, with light being the most important zeitgeber of the circadian system. Throughout the day, people are exposed to various scenes differing in light level, spectral composition and spatio-temporal properties. Personalized light exposure can be measured through wearable light loggers and dosimeters, including wrist-worn actimeters containing light sensors, yielding time series of an individual's light exposure. There is growing interest in relating light exposure patterns to health outcomes, requiring analytic techniques to summarize light exposure properties. Building on the previously published Python-based pyActigraphy module, here we introduce the module pyLight. This module allows users to extract light exposure data recordings from a wide range of devices. It also includes software tools to clean and filter the data, and to compute common metrics for quantifying and visualizing light exposure data. For this tutorial, we demonstrate the use of pyLight in one example dataset with the following processing steps: (1) loading, accessing and visual inspection of a publicly available dataset, (2) truncation, masking, filtering and binarization of the dataset, (3) calculation of summary metrics, including time above threshold (TAT) and mean light timing above threshold (MLiT). The pyLight module paves the way for open-source, large-scale automated analyses of light-exposure data.

Acute effects of light during daytime on central aspects of attention and affect: A systematic review

Light regulates both image- and various non-image forming responses in humans, including acute effects on attention and affect. To advance the understanding of light's immediate effects, this systematic review describes the acute effects of monochromatic/narrow bandwidth and polychromatic white light during daytime on distinct aspects of attention (alertness, sustained attention, working memory, attentional control and flexibility), and measures of affect (self-report measures, performance-based tests, psychophysiological measures) in healthy, adult human subjects. Original, peer-reviewed (quasi-) experimental studies published between 2000 and May 2024 were included according to predefined inclusion and exclusion criteria. Study quality was assessed, and results were synthesized across aspects of attention and affect and grouped according to light interventions; monochromatic/narrowband-width or polychromatic white light (regular white, bright white, and white with high correlated color temperature (CCT)). Results from included studies (n = 62) showed that alertness and working memory were most affected by light. Electroencephalographic markers of alertness improved the most with exposure to narrow bandwidth long-wavelength light, regular white, and white light with high CCT. Self-reported alertness and measures of working memory improved the most with bright white light. Results from studies testing the acute effects on sustained attention and attentional control and flexibility were inconclusive. Performance-based and psychophysiological measures of affect were only influenced by narrow bandwidth long-wavelength light. Polychromatic white light exerted mixed effects on self-reported affect. Studies were strongly heterogeneous in terms of light stimuli characteristics and reporting of light stimuli and control of variables influencing light's acute effects.

The effects of daylight duration on the multiple sleep latency test (MSLT) results: A pilot study

OBJECTIVE

MSLT results are known to be affected by multiple factors including sleep time, frequency of nighttime arousals, and medications intake. Although being the main synchronizer of sleep and wakefulness, daylight duration effects on MSLT have not been examined. Burlington, Vermont, USA experiences great variations in daylight duration, ranging from 8 h 50 min to 15 h 33 min of daylight. The aim of this study was to test the hypothesis that there would be photoperiod duration effects on MSLTs performed during short daylight (short daylight studies, SDS) vs. long daylight (long daylight studies, LDS) from 2013 to 2023 in our sleep laboratory.

METHODS

We identified and analyzed 37 SDS (daylight 530-560 min) and 36 LDS (daylight 903-933 min) from our database. Groups of SDS and LDS results were compared using non-paired student T test, Chi-Square and non-parametric Mann Whitney U Test.

RESULTS

Average daylight duration was 15 h 18 ± 14.6 min for LDS and 8 h 57 ± 18 min for SDS. Two groups did not differ in terms of the age, gender, BMI and race of patients studied. Mean total sleep time and sleep efficiency during PSG preceding MSLT, and MSLT mean sleep onset latency did not significantly differ for the two groups. However, SDS MSLT naps had significantly more sleep onset REM periods (SOREMP), and distribution of the number of SOREMP captured during MSLT was different for SDS and LDS groups. Differences of SDS and LDS results did not relate to sleep architecture of the overnight PSG as analysis of sleep and REM latency and relative percentages of N1, N2, REM, and N3 was not significantly different between SDS and LDS. The two groups showed difference in arousal indexes during N1 and REM sleep.

CONCLUSIONS

Daylight duration may impact MSLT results and should probably be accounted for in MSLT interpretation. Attention to photoperiod could be considered in MSLT guidelines, if our results are replicated in larger samples.

Metadata recommendations for light logging and dosimetry datasets

Background

Light exposure significantly impacts human health, regulating our circadian clock, sleep-wake cycle and other physiological processes. With the emergence of wearable light loggers and dosimeters, research on real-world light exposure effects is growing. There is a critical need to standardize data collection and documentation across studies.

Results

This article proposes a new metadata descriptor designed to capture crucial information within personalized light exposure datasets collected with wearable light loggers and dosimeters. The descriptor, developed collaboratively by international experts, has a modular structure for future expansion and customization. It covers four key domains: study design, participant characteristics, dataset details, and device specifications. Each domain includes specific metadata fields for comprehensive documentation. The user-friendly descriptor is available in JSON format. A web interface simplifies generating compliant JSON files for broad accessibility. Version control allows for future improvements.

Conclusions

Our metadata descriptor empowers researchers to enhance the quality and value of their light dosimetry datasets by making them FAIR (findable, accessible, interoperable and reusable). Ultimately, its adoption will advance our understanding of how light exposure affects human physiology and behaviour in real-world settings.

One seasonal clock fits all?

Adaptation of physiology and behavior to seasonal changes in the environment are for many organisms essential for survival. Most of our knowledge about the underlying mechanisms comes from research on photoperiodic regulation of reproduction in plants, insects and mammals. However, even humans, who mostly live in environments with minimal seasonal influences, show annual rhythms in physiology (e.g., immune activity, brain function), behavior (e.g., sleep-wake cycles) and disease prevalence (e.g., infectious diseases). As seasonal variations in environmental conditions may be drastically altered due to climate change, the understanding of the mechanisms underlying seasonal adaptation of physiology and behavior becomes even more relevant. While many species have developed specific solutions for dedicated tasks of photoperiodic regulation, we find a number of common principles and mechanisms when comparing insect and mammalian systems: (1) the circadian system contributes to photoperiodic regulation; (2) similar signaling molecules (VIP and PDF) are used for transferring information from the circadian system to the neuroendocrine system controlling the photoperiodic response; (3) the hormone melatonin participates in seasonal adaptation in insects as well as mammals; and (4) changes in photoperiod affect neurotransmitter function in both animal groups. The few examples of overlap elaborated in this perspective article, as well as the discussion on relevance for humans, should be seen as encouragement to unravel the machinery of seasonal adaptation in a multitude of organisms.

Myopia Control: Are We Ready for an Evidence Based Approach?

INTRODUCTION

Myopia and its vision-threatening complications present a significant public health problem. This review aims to provide an updated overview of the multitude of known and emerging interventions to control myopia, including their potential effect, safety, and costs.

METHODS

A systematic literature search of three databases was conducted. Interventions were grouped into four categories: environmental/behavioral (outdoor time, near work), pharmacological (e.g., atropine), optical interventions (spectacles and contact lenses), and novel approaches such as red-light (RLRL) therapies. Review articles and original articles on randomized controlled trials (RCT) were selected.

RESULTS

From the initial 3224 retrieved records, 18 reviews and 41 original articles reporting results from RCTs were included. While there is more evidence supporting the efficacy of low-dose atropine and certain myopia-controlling contact lenses in slowing myopia progression, the evidence about the efficacy of the newer interventions, such as spectacle lenses (e.g., defocus incorporated multiple segments and highly aspheric lenslets) is more limited. Behavioral interventions, i.e., increased outdoor time, seem effective for preventing the onset of myopia if implemented successfully in schools and homes. While environmental interventions and spectacles are regarded as generally safe, pharmacological interventions, contact lenses, and RLRL may be associated with adverse effects. All interventions, except for behavioral change, are tied to moderate to high expenditures.

CONCLUSION

Our review suggests that myopia control interventions are recommended and prescribed on the basis of accessibility and clinical practice patterns, which vary widely around the world. Clinical trials indicate short- to medium-term efficacy in reducing myopia progression for various interventions, but none have demonstrated long-term effectiveness in preventing high myopia and potential complications in adulthood. There is an unmet need for a unified consensus for strategies that balance risk and effectiveness for these methods for personalized myopia management.

Seasonal and Annual Change in Physiological Ocular Growth of 7- to 11-Year-Old Norwegian Children

Purpose

To investigate seasonal and annual change in physiological eye growth in Norwegian school children.

Methods

Measurements of ocular biometry, non-cycloplegic spherical equivalent autorefraction (SER), and choroidal thickness (ChT) were obtained for 92 children (44 females) aged 7 to 11 years at four time points over a year (November 2019-November 2020). Seasons (3- and 5-month intervals) were classified as winter (November-January), winter-spring (January-June), and summer-autumn (June-November). Cycloplegic SER was obtained in January and used to group children. The seasonal and annual changes were tested with a linear mixed-effects model (P values were adjusted for multiple comparisons).

Results

All the children experienced annual ocular growth, irrespective of SER, but less so during the summer-autumn. The baseline SER was lower (P < 0.001), axial length (AL) was longer (P < 0.038), and choroids were thicker in 10- to 11-year-old than 7- to 8-year-old mild hyperopes (P = 0.002). Assuming mild hyperopes (n = 65) experience only physiological eye growth, modeling revealed seasonal and annual increases in AL across sex and age (P < 0.018), with less change during the summer-autumn than winter-spring. The 7- to 8-year-olds had a larger decrease annually and over winter-spring in SER (P ≤ 0.036) and in ChT over winter-spring than the 10- to 11-year-olds (P = 0.006).

Conclusions

There were significant seasonal and annual changes in AL in children who had physiological eye growth irrespective of age within this cohort. Annual changes in SER and seasonal choroidal thinning were only observed in 7- to 8-year-old children. This indicates continued emmetropization in 7- to 8-year-olds and a transition to maintaining emmetropia in 10- to 11-year-olds.

Indoor and outdoor human behavior and myopia: an objective and dynamic study

Significance

Myopia holds significant public health concern given its social, ocular disease and economic burdens. Although environmental factors are primarily to blame for the rapid rise in prevalence, key risk factors remain unresolved.

Purpose

The aim of this study was to objectively characterize, using a wearable technology, the temporal indoor and outdoor behavioral patterns and associated environmental lighting characteristics of young myopic and nonmyopic University students.

Methods

Participants were recruited to continuously wear an Actiwatch for 3 weeks, during either or both academic and non-academic periods. The device allows continuous recording of activity and incident light. Recorded illuminance levels were used as a proxy for outdoors (>1,000 lux), with the dynamics (interval frequency and duration) of indoor and outdoor activities, as well as lighting characteristics derived. In addition, participant input regarding near work was obtained daily. Participants were classified by both myopia and axial length status (based on collected refractive error and biometry data) for the purpose of data analysis.

Result

A total of 55 students, aged 18 to 25 years of age, participated. Overall, the dosing of indoor and outdoor activities was similar across participants, regardless of myopia status, during the academic period. Nonetheless, an apparent difference in the timing of outdoor activities was noted with myopes going outdoors later in the day, particularly during the weekend (p = 0.03). While a trend was observed between increased lighting levels experienced outdoors and shorter axial lengths, there was no significant relationship with myopia status. Noteworthy, participants generally significantly overestimated time spent outdoors, compared to Actiwatch-derived estimates of the same.

Conclusion

While the findings from this cohort of young adult students did not reveal substantial myopia-related differences in behavior, the power of a more objective and dynamic approach to quantifying behavior cannot be understated, providing argument for general adoption of wearable technologies in future clinical myopia studies.

Seasonal variations of functional connectivity of human brains

Seasonal variations have long been observed in various aspects of human life. While there is an abundance of research that has characterized seasonality effects in, for example, cognition, mood, and behavior, including studies of underlying biophysical mechanisms, direct measurements of seasonal variations of brain functional activities have not gained wide attention. We have quantified seasonal effects on functional connectivity as derived from MRI scans. A cohort of healthy human subjects was divided into four groups based on the seasons of their scanning dates as documented in the image database of the Human Connectome Project. Sinusoidal functions were used as regressors to determine whether there were significant seasonal variations in measures of brain activities. We began with the analysis of seasonal variations of the fractional amplitudes of low frequency fluctuations of regional functional signals, followed by the seasonal variations of functional connectivity in both global- and network-level. Furthermore, relevant environmental factors, including average temperature and daylength, were found to be significantly associated with brain functional activities, which may explain how the observed seasonal fluctuations arise. Finally, topological properties of the brain functional network also showed significant variations across seasons. All the observations accumulated revealed seasonality effects of human brain activities in a resting-state, which may have important practical implications for neuroimaging research.

Effects of blue light exposure on ocular parameters and choroidal blood perfusion in Guinea pig

PURPOSE

To investigate the impact of different duration of blue light exposure on ocular parameters and choroidal blood perfusion in guinea pigs with lens-induced myopia.

METHOD

Three-week-old Guinea pigs were randomly assigned to different light-environment groups. All groups were subjected to 12-h light/dark cycle. The control (NC) group was conditioned without intervention. While lens-induced myopia (LIM) groups had a -10D lens placed in the right eye and 0D in the left eye. The guinea pigs were exposed to increasing periods of blue-light (420 nm) environment for 3,6,9,12 h per day. Changes in refraction, axial length (AL), the radius of corneal curvature (CCR), choroidal thickness (ChT), and choroidal blood perfusion (ChBP)were measured in both LIM-eye and fellow-eye during the second and fourth week of LIM duration.

RESULTS

During the first two weeks of the experiment, blue light exposure raised ChBP and ChT, and the effect of suppressing myopia was proportional to the duration of blue light exposure. However, in the fourth week of the experiment, prolonged blue light (12BL) exposure led to a reduction in retinal thickness and the increase in ChT and ChBP ceased. Shorter blue light exposure had a better effect on myopia suppression, with all blue light groups statistically different from the LIM group.

CONCLUSION

Exposure to blue-light appears to have the potential to improve ChBP and ChT, thereby inhibiting the development of myopia. we speculate that blue-light inhibits the development of myopia for reasons other than longitudinal chromatic aberration (LCA). However,long-term exposure to blue-light may have adverse effects on ocular development. The next step is to investigate in depth the mechanisms by which the rational use of blue light regulates choroidal blood flow, offering new hope for the treatment of myopia.

Variation in supplemental lighting quality influences key aroma volatiles in hydroponically grown 'Italian Large Leaf' basil

The spectral quality of supplemental greenhouse lighting can directly influence aroma volatiles and secondary metabolic resource allocation (i.e., specific compounds and classes of compounds). Research is needed to determine species-specific secondary metabolic responses to supplemental lighting (SL) sources with an emphasis on variations in spectral quality. The primary objective of this experiment was to determine the impact of supplemental narrowband blue (B) and red (R) LED lighting ratios and discrete wavelengths on flavor volatiles in hydroponic basil (Ocimum basilicum var. Italian Large Leaf). A natural light (NL) control and different broadband lighting sources were also evaluated to establish the impact of adding discrete and broadband supplements to the ambient solar spectrum. Each SL treatment provided 8.64 mol^.m^-2.d^-1 (100 µmol^.m^-2.s^-1, 24 h^.d^-1) photon flux. The daily light integral (DLI) of the NL control averaged 11.75 mol^.m^-2.d^-1 during the growth period (ranging from 4 to 20 mol^.m^-2.d^-1). Basil plants were harvested 45 d after seeding. Using GC-MS, we explored, identified, and quantified several important volatile organic compounds (VOCs) with known influence on sensory perception and/or plant physiological processes of sweet basil. We found that the spectral quality from SL sources, in addition to changes in the spectra and DLI of ambient sunlight across growing seasons, directly influence basil aroma volatile concentrations. Further, we found that specific ratios of narrowband B/R wavelengths, combinations of discrete narrowband wavelengths, and broadband wavelengths directly and differentially influence the overall aroma profile as well as specific compounds. Based on the results of this study, we recommend supplemental 450 and 660 nm (± 20 nm) wavelengths at a ratio of approximately 10B/90R at 100-200 µmol^.m^-2.s^-1, 12-24 h^.d^-1 for sweet basil grown under standard greenhouse conditions, with direct consideration of the natural solar spectrum and DLI provided for any given location and growing season. This experiment demonstrates the ability to use discrete narrowband wavelengths to augment the natural solar spectrum to provide an optimal light environment across variable growing seasons. Future experiments should investigate SL spectral quality for the optimization of sensory compounds in other high-value specialty crops.

Light as a Modulator of Non-Image-Forming Brain Functions—Positive and Negative Impacts of Increasing Light Availability

Light use is rising steeply, mainly because of the advent of light-emitting diode (LED) devices. LEDs are frequently blue-enriched light sources and may have different impacts on the non-image forming (NIF) system, which is maximally sensitive to blue-wavelength light. Most importantly, the timing of LED device use is widespread, leading to novel light exposure patterns on the NIF system. The goal of this narrative review is to discuss the multiple aspects that we think should be accounted for when attempting to predict how this situation will affect the NIF impact of light on brain functions. We first cover both the image-forming and NIF pathways of the brain. We then detail our current understanding of the impact of light on human cognition, sleep, alertness, and mood. Finally, we discuss questions concerning the adoption of LED lighting and screens, which offer new opportunities to improve well-being, but also raise concerns about increasing light exposure, which may be detrimental to health, particularly in the evening.

Ginkgo biloba extracts improve choroidal circulation leading to suppression of myopia in mice

Myopia is becoming more common across the world, necessitating the development of preventive methods. We investigated the activity of early growth response 1 (EGR-1) protein and discovered that Ginkgo biloba extracts (GBEs) activated EGR-1 in vitro. In vivo, C57BL/6 J mice were fed either normal or 0.0667% GBEs (200 mg/kg) mixed chow (n = 6 each), and myopia was induced with - 30 diopter (D) lenses from 3 to 6 weeks of age. Refraction and axial length were measured by an infrared photorefractor and an SD-OCT system, respectively. In lens-induced myopia mice, oral GBEs significantly improved refractive errors (- 9.92 ± 1.53 D vs. - 1.67 ± 3.51 D, p < 0.001) and axial elongation (0.22 ± 0.02 mm vs. 0.19 ± 0.02 mm, p < 0.05). To confirm the mechanism of GBEs in preventing myopia progression, the 3-week-old mice were divided into normally fed with either myopic-induced or non-myopic-induced groups and GBEs fed with either myopic-induced or non-myopic-induced groups (n = 10 each). Choroidal blood perfusion was measured with optical coherence tomography angiography (OCTA). In both non-myopic induced groups, compared to normal chow, oral GBEs significantly improved choroidal blood perfusion (8.48 ± 15.75%Area vs. 21.74 ± 10.54%Area, p < 0.05) and expression of Egr-1 and endothelial nitric oxide synthase (eNOS) in the choroid. In both myopic-induced groups, compared to normal chow, oral GBEs also improved choroidal blood perfusion (- 9.82 ± 9.47%Area vs. 2.29 ± 11.84%Area, p < 0.05) and was positively correlated with the change in choroidal thickness. These findings suggest that GBEs may inhibit the progression of myopia by improving choroidal blood perfusion.

Development of smart spectacles to monitor and modify myopia-related health behaviour in children

PURPOSE

To develop a wearable, spectacle-mounted, sensor-based device to monitor and modify myopia risk factors in children, namely near-working distance, light levels and spectral composition.

METHODS

A wearable, spectacle-mounted device has been developed, which consists of inbuilt sensors, namely: (i) light sensor to detect ambient light intensity; (ii) proximity sensor to measure near-work distance; (iii) microspectrograph to measure spectral power for six visible channels, namely red, green, blue, yellow, orange and violet and (iv) a global positioning system tracker to track the location and the device. The sensors were programmed by Arduino Nano, and the circuit was fixed onto a printed circuit board fitted onto a spectacle frame for pilot testing. Laboratory testing of the prototype was performed using a mannequin. An alert will be set when exceeding the predetermined threshold to help control myopia risk factors.

RESULTS

The indoor and outdoor light levels measured using the prototype were less than and greater than 1000 lux, respectively. The actual target distance and the corresponding distance measured by the prototype were highly correlated (R²  = 0.99). The mean distance measured by the prototype was within 1.5 cm of the actual target distance for distances between 30 and 95 cm. The spectral energy of the indoor location was highest for the orange channel at about 100-160 counts/μW/cm² , whereas it was highest for the blue channel in outdoor daylight (10,000-19,000 counts/μW/cm² ).

CONCLUSION

A working prototype that can simultaneously measure the viewing distance, light intensity and spectral composition has been developed.

Influence of location, season and time of day on the spectral composition of ambient light: Investigation for application in myopia

PURPOSE

Given the possible role of spectral composition of light and myopia, this study aimed at investigating the variation in the spectral composition of ambient light in different (a) outdoor/indoor locations, (b) time of a day and (c) seasons.

METHODS

The spectral power distribution (SPD), categorised into short (380-500 nm), middle (505-565 nm) and long wavelengths (625-780 nm), was recorded using a handheld spectrometer at three outdoor locations ('open playground', 'under shade of tree' and 'canopy') and three indoor locations ('room with multiple windows', 'closed room' and 'closed corridor'). Readings were taken at five different time points (3-h intervals between 6:30 and 18:00 hours) on two days, each during the summer and monsoon seasons.

RESULTS

The overall median SPD (IQR [25th-75th percentile] W/nm/m² ) across the three outdoor locations (0.11 [0.09, 0.12]) was 157 times higher than that of the indoor locations (0.0007 [0.0001, 0.001]). Considerable locational, diurnal and seasonal variation was observed in the distribution of the median SPD value, with the highest value being recorded in the 'open playground' (0.27 [0.21, 0.28]) followed by 'under shade of tree' (0.083 [0.074, 0.09]), 'canopy' (0.014 [0.012, 0.015]) and 'room with multiple windows' (0.023 [0.015, 0.028]). The relative percentage composition of short, middle and long wavelengths was similar in both the outdoor and indoor locations, with the proportion of middle wavelengths significantly higher (p < 0.01) than short and long wavelengths in all the locations, except 'canopy'.

CONCLUSION

Irrespective of variation in SPD values with location, time, day and season, outdoor locations always exhibited significantly higher spectral power than indoor locations. The relative percentage composition of short, middle and long wavelengths of light was similar across all locations. These findings establish a foundation for future research to understand the relationship between spectral power and the development of myopia.

Usability and Acceptability of a Corneal-Plane α-Opic Light Logger in a 24-h Field Trial

Introduction

Exposure to light fundamentally influences human physiology and behaviour by synchronising our biological clock to the external light-dark cycle and controlling melatonin production. In addition to well-controlled laboratory studies, more naturalistic approaches to examining these "non-visual" effects of light have been developed in recent years. As naturalistic light exposure is quite unlike well-controlled stimulus conditions in the laboratory, it is critical to measure light exposure in a person-referenced way, the "spectral diet." To this end, light loggers have been developed to capture personalised light exposure. As an alternative to light sensors integrated into wrist-worn actimeters, pendants, or brooch-based light loggers, a recently developed wearable light logger laterally attached to spectacle frames enables the measurement of biologically relevant quantities in the corneal plane.

Methods

Here, we examine the usability and acceptability of using the light logger in an undergraduate student sample (n = 18, mean±1SD: 20.1 ± 1.7 years; 9 female; Oxford, UK) in real-world conditions during a 24-h measurement period. We probed the acceptability of the light logger using rating questionnaires and open-ended questions.

Results

Our quantitative results show a modest acceptability of the light logger. A thematic analysis of the open-ended questions reveals that the form factor of the device, in particular, size, weight, and stability, and reactions from other people to the wearer of the light logger, were commonly mentioned aspects.

Conclusion

In sum, the results indicate the miniaturisation of light loggers and "invisible" integration into extant everyday objects as key areas for future technological development, facilitating the availability of light exposure data for developing personalised intervention strategies in both research, clinical and consumer contexts.

Development and validation of a 'MyLyt' wearable light tracking device

PURPOSE

We developed a clip-on light tracker (MyLyt) for estimating light exposure in real time. This study aimed at validating and investigating the feasibility of using MyLyt in children and adults.

METHOD

The study was conducted in two phases. Phase 1 involved validation against a factory-calibrated digital lux meter in three separate conditions: controlled environmental set-up, outdoors and indoors where intra-test (two measurements by the same tracker), inter-test (measurements among trackers) and inter-device (MyLyt tracker and lux meter) validations were conducted. Phase 2 involved a feasibility study where MyLyt was used in a real-world setting by 21 adults and 8 children. Participants were asked to log their real-time movements in an 'activity diary', which were correlated with the lux levels measured by the tracker.

RESULTS

A strong positive correlation and non-significant difference in the recorded mean illuminance levels were observed during intra-test (inter-class correlation: 1.00, p = 0.99), inter-test (0.91-1.00, p > 0.15) and inter-device (0.91-1.00, p > 0.56) validation in all three testing conditions (p > 0.49), except the indoor location. While the lux level measured by MyLyt was significantly higher than that of the lux meter (p < 0.01) in the indoor locations, differences were minimal and clinically insignificant. A Bland-Altman plot showed a minimal mean difference (95% limits of agreement) between the MyLyt tracker and lux meter in all three conditions (controlled environmental set-up: 641 [-949, 2230], outdoor: 74 [-2772, 2920] and indoor: -35 [-151, 80] lux). Phase 2 validation showed an expected illuminance level against the corresponding location with high sensitivity (97.8%) and specificity (99%) to accurately differentiate between outdoor and indoor locations.

CONCLUSION

The MyLyt tracker showed good repeatability, strong correlation and comparable values with the lux meter in the three tested conditions, making it suitable for tracking light exposure patterns for both research and clinical purposes.

The Association of Vitamin D and Its Pathway Genes’ Polymorphisms with Hypertensive Disorders of Pregnancy: A Prospective Cohort Study

Objective: We aimed to explore the effect of single nucleotide polymorphism (SNP) in the genes of the vitamin D (VitD) metabolic pathway and its interaction with VitD level during pregnancy on the development of hypertensive disorders of pregnancy (HDP). Methods: The study was conducted in the Zhoushan Maternal and Child Health Care Hospital, China, from August 2011 to May 2018. The SNPs in VitD metabolic pathway-related genes were genotyped. Plasma 25-hydroxyvitamin vitamin D (25(OH)D) levels was measured at first (T1), second (T2), and third (T3) trimesters. The information of systolic blood pressure (SBP) and diastolic blood pressure (DBP), and the diagnosis of HDP were extracted from the electronic medical record system. Multivariable linear and logistic regression models and crossover analysis were applied. Results: The prospective cohort study included 3699 pregnant women, of which 105 (2.85%) were diagnosed with HDP. After adjusting for potential confounders, VitD deficiency at T2, as well as the change of 25(OH)D level between T1 and T2, were negatively associated with DBP at T2 and T3, but not HDP. Polymorphisms in CYP24A1, GC, and LRP2 genes were associated with blood pressure and HDP. In addition, VitD interacted with CYP24A1, GC, and VDR genes’ polymorphisms on blood pressure. Furthermore, participants with polymorphisms in CYP24A1-rs2248137, LRP2-rs2389557, and LRP2-rs4667591 and who had VitD deficiency at T2 showed an increased risk of HDP. Conclusions: The individual and interactive association between VitD deficiency during pregnancy and SNPs in the genes of the VitD metabolic pathway on blood pressure and HDP were identified.

Candidate pathways for retina to scleral signaling in refractive eye growth

The global prevalence of myopia, or nearsightedness, has increased at an alarming rate over the last few decades. An eye is myopic if incoming light focuses prior to reaching the retinal photoreceptors, which indicates a mismatch in its shape and optical power. This mismatch commonly results from excessive axial elongation. Important drivers of the myopia epidemic include environmental factors, genetic factors, and their interactions, e.g., genetic factors influencing the effects of environmental factors. One factor often hypothesized to be a driver of the myopia epidemic is environmental light, which has changed drastically and rapidly on a global scale. In support of this, it is well established that eye size is regulated by a homeostatic process that incorporates visual cues (emmetropization). This process allows the eye to detect and minimize refractive errors quite accurately and locally over time by modulating the rate of elongation of the eye via remodeling its outermost coat, the sclera. Critically, emmetropization is not dependent on post-retinal processing. Thus, visual cues appear to influence axial elongation through a retina-to-sclera, or retinoscleral, signaling cascade, capable of transmitting information from the innermost layer of the eye to the outermost layer. Despite significant global research interest, the specifics of retinoscleral signaling pathways remain elusive. While a few pharmacological treatments have proven to be effective in slowing axial elongation (most notably topical atropine), the mechanisms behind these treatments are still not fully understood. Additionally, several retinal neuromodulators, neurotransmitters, and other small molecules have been found to influence axial length and/or refractive error or be influenced by myopigenic cues, yet little progress has been made explaining how the signal that originates in the retina crosses the highly vascular choroid to affect the sclera. Here, we compile and synthesize the evidence surrounding three of the major candidate pathways receiving significant research attention - dopamine, retinoic acid, and adenosine. All three candidates have both correlational and causal evidence backing their involvement in axial elongation and have been implicated by multiple independent research groups across diverse species. Two hypothesized mechanisms are presented for how a retina-originating signal crosses the choroid - via 1) all-trans retinoic acid or 2) choroidal blood flow influencing scleral oxygenation. Evidence of crosstalk between the pathways is discussed in the context of these two mechanisms.

Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults

Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, international standard provides a SI-compliant way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert scientific consensus and expressed in an easily measured quantity (melanopic equivalent daylight illuminance (melaponic EDI)) defined within this standard. The recommendations are supported by detailed analysis of the sensitivity of human circadian, neuroendocrine, and alerting responses to ocular light and provide a straightforward framework to inform lighting design and practice.

Weekly and seasonal variation in the circadian melatonin rhythm in humans: A response

We read with interest the commentary by Skeldon and Dijk about our article "Weekly, seasonal and chronotype-dependent variation of dim light melatonin onset." The discussion points raised by Skeldon and Dijk are currently among the most hotly debated in human circadian science. What external factors determine human phase of entrainment? How great is the contribution of natural versus artificial light and sun time versus social time? Our intra-individual data add to the still limited evidence from field studies in this matter. In their commentary, Skeldon and Dijk formulate two either-or hypotheses, postulating that humans entrain either solely to the natural light-dark cycle (sun time referenced by midday) (H₁ ) or solely to the light selected by local clock time and social constraints (H₂ ). Neither hypothesis accounts for the effect of season on human light exposure. We interpreted our findings along more complex lines, speculating that the 1-h earlier melatonin rise in summer found in our sample is likely the combined result of daylight saving time (DST)-induced behavioral advances and a stronger natural zeitgeber in summer (light exposure determined by social and seasonal factors, H_original ). Here, we show how the criticism by Skeldon and Dijk is based on two sentences quoted out of context (misrepresenting our hypothesis as H₁ ) and that their hypothesis H₂  leaves out important seasonal components in light exposure.

Individual differences and diversity in human physiological responses to light

Exposure to light affects our physiology and behaviour through a pathway connecting the retina to the circadian pacemaker in the hypothalamus - the suprachiasmatic nucleus (SCN). Recent research has identified significant individual differences in the non-visual effects of light,mediated by this pathway. Here, we discuss the fundamentals and individual differences in the non-visual effects of light. We propose a set of actions to improve our evidence database to be more diverse: understanding systematic bias in the evidence base, dedicated efforts to recruit more diverse participants, routine deposition and sharing of data, and development of data standards and reporting guidelines.

The Drosophila circadian phase response curve to light: Conservation across seasonally relevant photoperiods and anchorage to sunset

Photic history, including the relative duration of day versus night in a 24-hour cycle, is known to influence subsequent circadian responses to light in mammals. Whether such modulation is present in Drosophila is currently unknown. To date, all photic phase-response curves (PRCs) generated from Drosophila have done so with animals housed under seasonally agnostic equatorial photoperiods with alternating 12-hour segments of light and darkness. However, the genus contains thousands of species, some of which populate high and low-latitude habitats (20-50° north or south of the Equator) where seasonal variations in the light-dark schedule are pronounced. Here, we address this disconnect by constructing the first high-resolution Drosophila seasonal atlas for light-induced circadian phase-resetting. Testing the light responses of over 4,000 Drosophila at 120 timepoints across 5 seasonally-relevant rectangular photoperiods (i.e., LD 8:16, 10:14, 12:12, 14:10, and 16:8; 24 hourly intervals surveyed in each), we determined that many aspects of the fly circadian PRC waveform are conserved with increasing daylength. Surprisingly though, irrespective of LD schedule, the start of the PRCs always remained anchored to the timing of subjective sunset, creating a differential overlap of the advance zone with the morning hours after subjective sunrise that was maximized under summer photoperiods and minimized under winter photoperiods. These data suggest that there may be differences in flies versus mammals as to how the photoperiod modulates the waveform and amplitude of the circadian PRC to light. On the other hand, they support the possibility that the lights-off transition determines the phase-positioning of photic PRCs across seasons and across species. More work is necessary to test this claim and whether it might factor into the timing of seasonal light responses in humans.

The Association of Gene Variants in the Vitamin D Metabolic Pathway and Its Interaction with Vitamin D on Gestational Diabetes Mellitus: A Prospective Cohort Study

The present prospective study included 2156 women and investigated the effect of gene variants in the vitamin D (VitD) metabolic and glucose pathways and their interaction with VitD levels during pregnancy on gestational diabetes mellitus (GDM). Plasma 25(OH)D concentrations were measured at the first and second trimesters. GDM subtype 1 was defined as those with isolated elevated fasting plasma glucose; GDM subtype 2 were those with isolated elevated postprandial glucose at 1 h and/or 2 h; and GDM subtype 3 were those with both elevated fasting plasma glucose and postprandial glucose. Six Gc isoforms were categorized based on two GC gene variants rs4588 and rs7041, including 1s/1s, 1s/2, 1s/1f, 2/2, 1f/2 and 1f/1f. VDR-rs10783219 and MTNR1B-rs10830962 were associated with increased risks of GDM and GDM subtype 2; interactions between each other as well as with CDKAL1-rs7754840 were observed (P_interaction < 0.05). Compared with the 1f/1f isoform, the risk of GDM subtype 2 among women with 1f/2, 2/2, 1s/1f, 1s/2 and 1s/1s isoforms and with prepregnancy body mass index ≥24 kg/m² increased by 5.11, 10.01, 10, 14.23, 19.45 times, respectively. Gene variants in VitD pathway interacts with VitD deficiency at the first trimester on the risk of GDM and GDM subtype 2.

Modified Plasma Cytokine Profile in Occupational Dermatitis

BACKGROUND

Despite significant progress in the diagnosis of contact dermatitis, the identification by specific tests or biomarkers remains an unsolved issue, particularly when needed for the confirmation of the occupational origin of the disease.

OBJECTIVE

To characterize the plasma proteome profile in occupational dermatitis in workers of paint industry.

METHODS

The study has a case-control design, comparing exposed workers with and without occupational contact dermatitis, matched for age, gender, occupational history, and comorbidities. An immunological assay (Human XL Cytokine Array Kit - ARY022B, R&D Systems) was used to measure the plasma levels of 105 cytokines and chemokines in a pooled sample of the cases and a pooled sample of the controls.

RESULTS

A 1.5-fold increase was noticed for interleukin 3, interleukin 10, and leptin in cases, as compared to controls. Fibroblast growth factor-7 and growth/differentiation factor-15 showed a 1.4-fold increase, while interleukin 19, interleukin 31, and macrophage inflammatory protein 3a.had only a 1.3- fold increase. The leukemia inhibitory factor was the only plasma cytokine that showed a 1.3-fold decrease. All other cytokines had a variation of less than 1.2-fold between cases and controls.

CONCLUSION

The recognition of the molecular signatures is very important for an accurate and indisputable diagnosis of occupational contact dermatitis. In workers from the paint industry, plasma levels of interleukins 3, 10, 13 and 19, fibroblast growth factor-7, and growth/differentiation factor-15, together with leukemia inducible factor, may differentiate subjects with contact dermatitis from those without skin lesions.

Myopia Progression as a Function of Sex, Age, and Ethnicity

Purpose

To model juvenile-onset myopia progression as a function of race/ethnicity, age, sex, parental history of myopia, and time spent reading or in outdoor/sports activity.

Methods

Subjects were 594 children in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study with at least three study visits: one visit with a spherical equivalent (SPHEQ) less myopic/more hyperopic than −0.75 diopter (D), the first visit with a SPHEQ of −0.75 D or more myopia (onset visit), and another after myopia onset. Myopia progression from the time of onset was modeled using cubic models as a function of age, race/ethnicity, and other covariates.

Results

Younger children had faster progression of myopia; for example, the model-estimated 3-year progression in an Asian American child was −1.93 D when onset was at age 7 years compared with −1.43 D when onset was at age 10 years. Annual progression for girls was 0.093 D faster than for boys. Asian American children experienced statistically significantly faster myopia progression compared with Hispanic (estimated 3-year difference of −0.46 D), Black children (−0.88 D), and Native American children (−0.48 D), but with similar progression compared with White children (−0.19 D). Parental history of myopia, time spent reading, and time spent in outdoor/sports activity were not statistically significant factors in multivariate models.

Conclusions

Younger age, female sex, and racial/ethnic group were the factors associated with faster myopic progression. This multivariate model can facilitate the planning of clinical trials for myopia control interventions by informing the prediction of myopia progression rates.

Weekly and seasonal variation in the circadian melatonin rhythm in humans: Entrained to local clock time, social time, light exposure or sun time?

A recent elegant study published in this journal (Zerbini, Winnebeck & Merrow, J Pineal Res, e12723, 2021) reported data on weekly and seasonal changes in circadian timing, as assessed by the melatonin rhythm in dim light in a population that was exposed to a change from standard time to day light saving time. The authors highlight a one hour earlier timing of melatonin onset in summer compared with winter and a 20 minutes delay on work-free days compared with work days. The variations in the timing of the melatonin rhythm are reported in standard time and the authors imply that the data are consistent with synchronization to midday and that "we know that humans entrain to sun time." Here, we show that their extensive data are most parsimoniously explained by entrainment to local clock time and associated light exposure rather than "sun time," indexed by either dawn or midday.

Long-Term Narrowband Lighting Influences Activity but Not Intrinsically Photosensitive Retinal Ganglion Cell-Driven Pupil Responses

Purpose: Light affects a variety of non-image forming processes, such as circadian rhythm entrainment and the pupillary light reflex, which are mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs). The purpose of this study was to assess the effects of long- and short-wavelength ambient lighting on activity patterns and pupil responses in rhesus monkeys. Methods: Infant rhesus monkeys were reared under either broadband "white" light (n = 14), long-wavelength "red" light (n = 20; 630 nm), or short-wavelength "blue" light (n = 21; 465 nm) on a 12-h light/dark cycle starting at 24.1 ± 2.6 days of age. Activity was measured for the first 4 months of the experimental period using a Fitbit activity tracking device and quantified as average step counts during the daytime (lights-on) and nighttime (lights-off) periods. Pupil responses to 1 s red (651 nm) and blue (456 nm) stimuli were measured after approximately 8 months. Pupil metrics included maximum constriction and the 6 s post-illumination pupil response (PIPR). Results: Activity during the lights-on period increased with age during the first 10 weeks (p < 0.001 for all) and was not significantly different for monkeys reared in white, red, or blue light (p = 0.07). Activity during the 12-h lights-off period was significantly greater for monkeys reared in blue light compared to those in white light (p = 0.02), but not compared to those in red light (p = 0.08). However, blue light reared monkeys exhibited significantly lower activity compared to both white and red light reared monkeys during the first hour of the lights-off period (p = 0.01 for both) and greater activity during the final hour of the lights-off period (p < 0.001 for both). Maximum pupil constriction and the 6 s PIPR to 1 s red and blue stimuli were not significantly different between groups (p > 0.05 for all). Conclusion: Findings suggest that long-term exposure to 12-h narrowband blue light results in greater disruption in nighttime behavioral patterns compared to narrowband red light. Normal pupil responses measured later in the rearing period suggest that ipRGCs adapt after long-term exposure to narrowband lighting.

Daytime light spectrum affects photoperiodic induction of vernal response in obligate spring migrants

It is not well understood how the spectral composition (wavelength) of daylight that varies considerably during the day and seasons affects photoperiodic responses in a seasonal species. Here, we investigated the molecular underpinnings of wavelength-dependent photoperiodic induction in migratory redheaded buntings transferred to 13 h long days in neutral (white), 460 nm (blue), 500 nm (green) or 620 nm (red) wavelength that were compared with one another, and to short day controls for indices of the migratory (body fattening and weight gain, and Zugunruhe) and reproductive (testicular maturation) responses. Buntings showed wavelength-dependent photoperiodic response, with delayed Zugunruhe and slower testis maturation under 620 nm red light. Post-mortem comparison of gene expressions further revealed wavelength-dependence of the photoperiodic molecular response. Whereas there were higher retinal expressions of opn2 (rhodopsin) and opn5 (neuropsin) genes in red daylight, and of rhodopsin-like opsin (rh2) gene in green daylight, the hypothalamic opn2 mRNA levels were higher in blue daylight. Similarly, we found in birds under blue daylight an increased hypothalamic expression of genes involved in the photoperiodic induction (thyroid stimulating hormone subunit beta, tshb; eye absent 3, eya3; deiodinase type 2, dio2) and associated neural responses such as the calcium signaling (ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 2, atp2a2), dopamine biosynthesis (tyrosine hydroxylase, th) and neurogenesis (brain-derived neurotrophic factor, bdnf). These results demonstrate transcriptional changes in parallel to responses associated with migration and reproduction in buntings, and suggest a role of daylight spectrum in photoperiodic induction of the vernal response in obligate spring avian migrants.

Weekly, seasonal, and chronotype-dependent variation of dim-light melatonin onset

In humans, the most important zeitgeber for entrainment is light. Laboratory studies have shown that meaningful changes in light exposure lead to phase shifts in markers of the circadian clock. In natural settings, light is a complex signal varying with external conditions and individual behaviors; nonetheless, phase of entrainment is assumed to be fairly stable. Here, we investigated the influence of season and weekly schedule (as indicators of variation in light landscapes) on phase of entrainment. Using a within-subjects design (N = 33), we assessed dim-light melatonin onset (DLMO) as a circadian phase marker in humans, on workdays and work-free days, in summer (under daylight saving time) and in winter, while also estimating sleep times from actimetry. Our mixed-model regressions show that both season and weekly structure are linked with changes in phase of entrainment and sleep. In summer, both DLMO and sleep times were about 1 hour earlier compared to winter, and sleep duration was shorter. On work-free days, DLMO and sleep times were later, and their phase relationship differed more relative to workdays. All these effects were stronger in later chronotypes (those who habitually sleep late). Our results confirm that phase of entrainment is earlier when stronger zeitgebers are present (summer) and show that it relates to midday or midnight rather than sunrise or sunset. Additionally, they suggest that late chronotypes are capable of rapid phase shifts each week as they move between workdays and work-free days, stimulating interesting questions about the stability of circadian phase under natural conditions.

Evaluating the timing of differences in activity related to depression symptoms across adulthood in the United States

BACKGROUND

Relative activity deficits found in people with (verses without) depression symptoms/disorders may accumulate uniformly throughout the day, or they may tend to be expressed at specific times. Evidence for the latter would suggest times when behavioral approaches are most needed to reduce depression and its health consequences.

METHODS

We performed a secondary-data analysis of participants who contributed valid accelerometer data at the 2005-2006 National Health and Nutrition Examination Survey (n=4390). Participants were categorized according to the Patient Health Questionnaire-9 standard cut-point of ≥10 (i.e., people with versus without clinically significant depression symptoms). Average levels of accelerometer-measured activity in two-hour bins were the dependent variable in mixed models testing if the relationship between depression status and activity level differed by time of day; and if any such relations varied by age group (18-29 years, 30-44 years, 45-59 years, and 60+ years).

RESULTS

In adults over the age of 30, people with depression symptoms had generally lower levels of activity across the day, but these effects were most markedly pronounced in the morning hours. We found no differences in activity levels associated with prevalent depression symptoms among people 18-30 years of age.

LIMITATIONS

Core aspects of depression pathophysiology that produce these different activity patterns and confer their effects on mood were not measured.

CONCLUSIONS

In adults 30 years and older, efforts to ameliorate relative activity deficits associated with depression may benefit from considering the apparently outsized role of inactivity that occurs in the morning.

Preliminary Results: The Impact of Smartphone Use and Short-Wavelength Light during the Evening on Circadian Rhythm, Sleep and Alertness

Smartphone usage strongly increased in the last decade, especially before bedtime. There is growing evidence that short-wavelength light affects hormonal secretion, thermoregulation, sleep and alertness. Whether blue light filters can attenuate these negative effects is still not clear. Therefore, here, we present preliminary data of 14 male participants (21.93 ± 2.17 years), who spent three nights in the sleep laboratory, reading 90 min either on a smartphone (1) with or (2) without a blue light filter, or (3) on printed material before bedtime. Subjective sleepiness was decreased during reading on a smartphone, but no effects were present on evening objective alertness in a GO/NOGO task. Cortisol was elevated in the morning after reading on the smartphone without a filter, which resulted in a reduced cortisol awakening response. Evening melatonin and nightly vasodilation (i.e., distal-proximal skin temperature gradient) were increased after reading on printed material. Early slow wave sleep/activity and objective alertness in the morning were only reduced after reading without a filter. These results indicate that short-wavelength light affects not only circadian rhythm and evening sleepiness but causes further effects on sleep physiology and alertness in the morning. Using a blue light filter in the evening partially reduces these negative effects.

Effects of Narrowband Light on Choroidal Thickness and the Pupil

Purpose

To determine the effects of narrowband light exposure on choroidal thickness and the pupil response in humans.

Methods

Twenty subjects, ages 21 to 43 years, underwent 1 hour of exposure to broadband, short wavelength “blue,” or long wavelength “red” light, or darkness. Choroidal thickness, imaged with spectral domain optical coherence tomography, axial length, determined from biometry, and rod/cone- and intrinsically photosensitive retinal ganglion cell-driven pupil responses were measured before and after exposure. Pupil stimuli were six 1 second alternating red (651 nm) and blue (456 nm) stimuli, 60 seconds apart. Pupil metrics included maximum constriction and the 6 second post-illumination pupil response (PIPR).

Results

Compared with before exposure, the choroid significantly thinned after broadband light, red light, and dark exposure (all P < 0.05), but not after blue light exposure (P = 0.39). The maximum constriction to 1 second red stimuli significantly decreased after all light exposures (all P < 0.001), but increased after dark exposure (P = 0.02), compared with before exposure. Maximum constriction and 6-second PIPR to 1 second blue stimuli significantly decreased after all light exposures compared with before exposure (all P < 0.005), with no change after dark exposure (P > 0.05). There were no differences in axial length change or 6-second PIPR to red stimuli between exposures.

Conclusions

Narrowband blue and red light exposure induced differential changes in choroidal thickness. Maximum constriction, a function of rod/cone activity, and the intrinsically photosensitive retinal ganglion cell-mediated PIPR were attenuated after all light exposures. Findings demonstrate differing effects of short-term narrowband light and dark exposure on the choroid, rod/cone activity, and intrinsically photosensitive retinal ganglion cells.

Circadian Photoentrainment in Mice and Humans

Light around twilight provides the primary entrainment signal for circadian rhythms. Here we review the mechanisms and responses of the mouse and human circadian systems to light. Both utilize a network of photosensitive retinal ganglion cells (pRGCs) expressing the photopigment melanopsin (OPN4). In both species action spectra and functional expression of OPN4 in vitro show that melanopsin has a λ_max close to 480 nm. Anatomical findings demonstrate that there are multiple pRGC sub-types, with some evidence in mice, but little in humans, regarding their roles in regulating physiology and behavior. Studies in mice, non-human primates and humans, show that rods and cones project to and can modulate the light responses of pRGCs. Such an integration of signals enables the rods to detect dim light, the cones to detect higher light intensities and the integration of intermittent light exposure, whilst melanopsin measures bright light over extended periods of time. Although photoreceptor mechanisms are similar, sensitivity thresholds differ markedly between mice and humans. Mice can entrain to light at approximately 1 lux for a few minutes, whilst humans require light at high irradiance (>100’s lux) and of a long duration (>30 min). The basis for this difference remains unclear. As our retinal light exposure is highly dynamic, and because photoreceptor interactions are complex and difficult to model, attempts to develop evidence-based lighting to enhance human circadian entrainment are very challenging. A way forward will be to define human circadian responses to artificial and natural light in the “real world” where light intensity, duration, spectral quality, time of day, light history and age can each be assessed.

Daily and Seasonal Variation in Light Exposure among the Old Order Amish

Exposure to artificial bright light in the late evening and early night, common in modern society, triggers phase delay of circadian rhythms, contributing to delayed sleep phase syndrome and seasonal affective disorder. Studying a unique population like the Old Order Amish (OOA), whose lifestyles resemble pre-industrial societies, may increase understanding of light’s relationship with health. Thirty-three participants (aged 25–74, mean age 53.5; without physical or psychiatric illnesses) from an OOA community in Lancaster, PA, were assessed with wrist-worn actimeters/light loggers for at least 2 consecutive days during winter/spring (15 January–16 April) and spring/summer (14 May–10 September). Daily activity, sleep–wake cycles, and their relationship with light exposure were analyzed. Overall activity levels and light exposure increased with longer photoperiod length. While seasonal variations in the amount and spectral content of light exposure were equivalent to those reported previously for non-Amish groups, the OOA experienced a substantially (~10-fold) higher amplitude of diurnal variation in light exposure (darker nights and brighter days) throughout the year than reported for the general population. This pattern may be contributing to lower rates of SAD, short sleep, delayed sleep phase, eveningness, and metabolic dysregulation, previously reported among the OOA population.

Short-Wavelength (Violet) Light Protects Mice From Myopia Through Cone Signaling

Purpose

Exposure to short-wavelength light influences refractive development and inhibits myopic development in many animal models. Retinal mechanisms underlying this response remain unknown. This study used a mouse model of lens-induced myopia to evaluate the effect of different wavelength light on refractive development and dopamine levels in the retina. A possible retinal pathway is tested using a mutant mouse with dysfunctional cones.

Methods

Wild-type C57BL/6J (WT) and ALS/LtJ/Gnat2^cpfl3 (Gnat2^−/−) mice were exposed to one of three different light conditions beginning at postnatal day 28: broad-spectrum “white” (420-680 nm), medium wavelength “green” (525 ± 40 nm), and short wavelength “violet” (400 ± 20 nm). One-half of the mice received hyperopic lens defocus. All mice were exposed to the light for 4 weeks; animals were measured weekly for refractive error and axial parameters. Retinal dopamine and the dopamine metabolite 3,4-dihydroxyphenylacetic acid were measured by HPLC.

Results

In WT mice, short-wavelength violet light induced hyperopia and violet light inhibited lens-induced myopia when compared with mice exposed to white light. Hyperopia could be attributed to shallower vitreous chambers in WT animals. There were no changes in the levels of dopamine or its metabolite. In Gnat2^−/− mice, violet light did not induce hyperopia or inhibit lens-induced myopia.

Conclusions

These findings show that short-wavelength light slows refractive eye growth, producing hyperopic responses in mice and inhibiting lens-induced myopia. The lack of inhibition in mice with dysfunctional cones suggests that cone signaling plays a role in the hyperopic response to short-wavelength (violet) light.

Association of Sunlight Exposure with Sleep Hours in Iranian Children and Adolescents: The CASPIAN-V Study

We aimed to assess the association of sunlight exposure with sleep duration and sleep onset time in children. Data were obtained from the fifth survey of a national school-based surveillance program in Iran. Sunlight exposure time, sleep duration, sleep onset time, physical activity time, mental health status and frequency of consuming coffee and tea were recorded. Overall, 14 274 students aged 7-18 years were recruited. Sleep duration was associated positively with sex, age, body mass index and physical activity, as well as with sunlight exposure and negatively with the consumption of coffee and tea. Higher physical activity, exposure to sunlight and mental status score in children exposed to sunlight via their face, hands, arms and feet, reduced the likelihood of sleep onset time after midnight (odds ratio (OR) = 0.909, 0.741 and 0.554 respectively). Daily exposure to sunlight may increase sleep duration and advance the sleep onset time in children and adolescents.

Depression Prediction by Using Ecological Momentary Assessment, Actiwatch Data, and Machine Learning: Observational Study on Older Adults Living Alone

BACKGROUND

Although geriatric depression is prevalent, diagnosis using self-reporting instruments has limitations when measuring the depressed mood of older adults in a community setting. Ecological momentary assessment (EMA) by using wearable devices could be used to collect data to classify older adults into depression groups.

OBJECTIVE

The objective of this study was to develop a machine learning algorithm to predict the classification of depression groups among older adults living alone. We focused on utilizing diverse data collected through a survey, an Actiwatch, and an EMA report related to depression.

METHODS

The prediction model using machine learning was developed in 4 steps: (1) data collection, (2) data processing and representation, (3) data modeling (feature engineering and selection), and (4) training and validation to test the prediction model. Older adults (N=47), living alone in community settings, completed an EMA to report depressed moods 4 times a day for 2 weeks between May 2017 and January 2018. Participants wore an Actiwatch that measured their activity and ambient light exposure every 30 seconds for 2 weeks. At baseline and the end of the 2-week observation, depressive symptoms were assessed using the Korean versions of the Short Geriatric Depression Scale (SGDS-K) and the Hamilton Depression Rating Scale (K-HDRS). Conventional classification based on binary logistic regression was built and compared with 4 machine learning models (the logit, decision tree, boosted trees, and random forest models).

RESULTS

On the basis of the SGDS-K and K-HDRS, 38% (18/47) of the participants were classified into the probable depression group. They reported significantly lower scores of normal mood and physical activity and higher levels of white and red, green, and blue (RGB) light exposures at different degrees of various 4-hour time frames (all P<.05). Sleep efficiency was chosen for modeling through feature selection. Comparing diverse combinations of the selected variables, daily mean EMA score, daily mean activity level, white and RGB light at 4:00 pm to 8:00 pm exposure, and daily sleep efficiency were selected for modeling. Conventional classification based on binary logistic regression had a good model fit (accuracy: 0.705; precision: 0.770; specificity: 0.859; and area under receiver operating characteristic curve or AUC: 0.754). Among the 4 machine learning models, the logit model had the best fit compared with the others (accuracy: 0.910; precision: 0.929; specificity: 0.940; and AUC: 0.960).

CONCLUSIONS

This study provides preliminary evidence for developing a machine learning program to predict the classification of depression groups in older adults living alone. Clinicians should consider using this method to identify underdiagnosed subgroups and monitor daily progression regarding treatment or therapeutic intervention in the community setting. Furthermore, more efforts are needed for researchers and clinicians to diversify data collection methods by using a survey, EMA, and a sensor.

Origins of Refractive Errors: Environmental and Genetic Factors

Refractive errors are the product of a mismatch between the axial length of the eye and its optical power, creating blurred vision. Uncorrected refractive errors are the second leading cause of worldwide blindness. One refractive error currently attracting significant scientific interest is myopia, mostly owing to the recent rise in its prevalence worldwide and associated ocular disease burden. This increase in myopia prevalence has also been rapid, suggesting environmental influences in addition to any genetic influences on eye growth. This review defines refractive errors, describes their prevalence, and presents evidence for the influence of genetic and environmental factors related to refractive error development.

Sleep Timing in Late Autumn and Late Spring Associates With Light Exposure Rather Than Sun Time in College Students

Timing of the human sleep-wake cycle is determined by social constraints, biological processes (sleep homeostasis and circadian rhythmicity) and environmental factors, particularly natural and electrical light exposure. To what extent seasonal changes in the light-dark cycle affect sleep timing and how this varies between weekdays and weekends has not been firmly established. We examined sleep and activity patterns during weekdays and weekends in late autumn (standard time, ST) and late spring (daylight saving time, DST), and expressed their timing in relation to three environmental reference points: clock-time, solar noon (SN) which occurs one clock hour later during DST than ST, and the midpoint of accumulated light exposure (50% LE). Observed sleep timing data were compared to simulated data from a mathematical model for the effects of light on the circadian and homeostatic regulation of sleep. A total of 715 days of sleep timing and light exposure were recorded in 19 undergraduates in a repeated-measures observational study. During each three-week assessment, light and activity were monitored, and self-reported bed and wake times were collected. Light exposure was higher in spring than in autumn. 50% LE did not vary across season, but occurred later on weekends compared to weekdays. Relative to clock-time, bedtime, wake-time, mid-sleep, and midpoint of activity were later on weekends but did not differ across seasons. Relative to SN, sleep and activity measures were earlier in spring than in autumn. Relative to 50% LE, only wake-time and mid-sleep were later on weekends, with no seasonal differences. Individual differences in mid-sleep did not correlate with SN but correlated with 50% LE. Individuals with different habitual bedtimes responded similarly to seasonal changes. Model simulations showed that light exposure patterns are sufficient to explain sleep timing in spring but less so in autumn. The findings indicate that during autumn and spring, the timing of sleep associates with actual light exposure rather than sun time as indexed by SN.

How Does Light Regulate Mood and Behavioral State?

The idea that light affects mood and behavioral state is not new. However, not much is known about the particular mechanisms and circuits involved. To fully understand these, we need to know what properties of light are important for mediating changes in mood as well as what photoreceptors and pathways are responsible. Increasing evidence from both human and animal studies imply that a specialized class of retinal ganglion cells, intrinsically photosensitive retinal ganglion cells (ipRGCs), plays an important role in the light-regulated effects on mood and behavioral state, which is in line with their well-established roles in other non-visual responses (pupillary light reflex and circadian photoentrainment). This paper reviews our current understanding on the mechanisms and paths by which the light information modulates behavioral state and mood.

Seasonal Variation in Bright Daylight Exposure, Mood and Behavior among a Group of Office Workers in Sweden

The purpose of the study was to investigate seasonal variation in mood and behavior among a group of office workers in Sweden (56°N). Thirty subjects participated in this longitudinal study. The subjects kept a weekly log that included questionnaires for ratings of psychological wellbeing and daily sleep-activity diaries where they also noted time spent outdoors. The lighting conditions in the offices were subjectively evaluated during one day, five times over the year. There was a seasonal variation in positive affect and in sleep-activity behavior. Across the year, there was a large variation in the total time spent outdoors in daylight. The subjects reported seasonal variation concerning the pleasantness, variation and strength of the light in the offices and regarding the visibility in the rooms. Finally, the subjects spent most of their time indoors, relying on artificial lighting, which demonstrates the importance of the lighting quality in indoor environments.

Non-visual effects of light: how to use light to promote circadian entrainment and elicit alertness

In addition to stimulating the visual system, light incident on the retina stimulates other biological functions, also referred to as non-visual responses. Among the most notable biological functions are human circadian rhythms, which are bodily rhythms that, in constant darkness, oscillate with a period close to, but typically slightly longer than 24 hours. Twenty-four-hour light-dark patterns incident on the retina are the major synchronizer of circadian rhythms to the local time on Earth. Entrainment of circadian rhythms has been implicated in health and well-being. Light can also elicit an acute alerting effect on people, similar to a "cup of coffee." This review summarizes the literature on how light affects entrainment and alertness and how it can be used to achieve these aims.

Impact of seasons on an individual's chronotype: current perspectives

Diurnal preference, or chronotype, determined partly by genetics and modified by age, activity, and the environment, defines the time of day at which one feels at his/her best, when one feels sleepy, and when one would prefer to start his/her day. Chronotype affects the phase relationship of an individual's circadian clock with the environment such that morning types have earlier-phased circadian rhythms than evening types. The phases of circadian rhythms are synchronized to the environment on a daily basis, undergoing minor adjustments of phase each day. Light is the most potent time cue for phase-shifting circadian rhythms, but the timing and amount of solar irradiation vary dynamically with season, especially with increasing distance from the equator. There is evidence that chronotype is modified by seasonal change, most likely due to the changes in the light environment, but interindividual differences in photoperiod responsiveness mean that some people are more affected than others. Differences in circadian light sensitivity due to endogenous biological reasons and/or previous light history are responsible for the natural variation in photoperiod responsiveness. Modern lifestyles that include access to artificial light at night, temperature-controlled environments, and spending much less time outdoors offer a buffer to the environmental changes of the seasons and may contribute to humans becoming less responsive to seasons.