Plain English Summary
Background and study aims
Humans are a diurnal species (active during daylight) usually exposed to light which is necessary not only for vision but also for regulating the sleep-wake cycle. This regulation is based on the neural system beginning in the retina through subcortical and cortical parts of the brain. This system is specifically sensitive to blue parts of the visual spectrum.
Ironically, in the consequence of the natural age-related process of eye lens yellowing, less blue light reaches the retina and the brain. This pivotal fact may be related to an age-related decline in four aspects of human functioning: sleep quality, circadian rhythmicity, cognitive and emotional processing. The aim of this study is to verify the effects of blue light blocking on healthy and young participants, who do not suffer the same detrimental processes as older adults.
Who can participate?
Young, healthy volunteers participated in the study. Inclusion criteria were age 20-35 yo, experience in contact lens wearing as well as no psychological or neurological conditions. We excluded those volunteers that did not meet criteria for MRI scan or had other that myopia eye conditions (ophthalmological examination was performed before starting the study).
What does the study involve?
The study involved conducting a series of functional MRI brain scans on a weekly basis with additional measurements related to sleep-wake cycle, such as wearing actigraphs, which monitor movement on a daily basis, filling several questionnaires and measuring hormonal level in saliva every week.
What are the possible benefits and risks of participating?
Participants could have experience worsening of their state of well-being - feeling sleepier during the day or having problems with falling asleep. Their emotional and cognitive functioning could also potentially deteriorate on a mild level.
The opposite effect - better sleep and, in consequence, feeling better during the day - may also be considered.
Where is the study run from?
Malopolska Centre of Biotechnology, Krakow, Poland
When is the study starting and how long is it expected to run for?
May 2015 to May 2017
Who is funding the study?
Narodowe Centrum Nauki (National Science Centre of Poland)
Who is the main contact?
Prof. Tadeusz Marek, email@example.com
The effects of long-term reduction of short wavelength light on circadian regulation, neural aspects of cognitive and affective functioning in humans - a behavioural, questionnaire, actigraphy, biochemical and neuroimaging study.
The following research questions were posed:
How does the condition of blocking the blue light influence sleep quality?
Will blue light reduction cause circadian rhythm desynchronization over time?
Will blue light reduction have impact on cognitive functioning and emotional state?
How does the condition of blocking the blue light influence neural activity related to cognitive processes?
How does the condition of blocking the blue light influence activation of brain structures involved in processing positive and negative emotions?
Approved 26/03/2013, Bioethics commission at the Polish Military Institute of Aviation Medicine (54/56 Krasińskiego Street, 01-755 Warsaw, Poland; +48 26 185 26 01; firstname.lastname@example.org), ref: 01/2013
Randomised parallel trial
Primary study design
Secondary study design
Randomised parallel trial
Quality of life
Patient information sheet
Not available in web format, please use contact details to request a participant information sheet.
Participants were young, healthy volunteers.
The study concerns young healthy volunteers, which were asked to wear blue light blocking lenses for the period of four weeks. Their functioning under the condition of blocking the blue light was compared to the control group wearing regular contact lenses. The study was planned to be conducted during spring to fall months to have a higher level of insolation.
The experiment lasted six weeks. For each participant, the measurements were obtained once a week on the same day of the week in the evenings. For the first two weeks, all participants wore regular, daily disposable contact lenses. At the first session, participants were familiarized with experimental procedures and the laboratory. The second session was treated as a baseline. For the next four weeks, participants wore monthly disposable contact lenses with different filter properties according to group. At each session, participants had MR scanning, they performed experimental tasks and filled in questionnaires. Also, saliva samples were collected. During the whole 6 weeks, participants wore actigraphs.
Participants assigned to BLB group wore the amber contact lenses reducing the transmittance of BL by approximately 90% on the 24-hour basis (UltraVision, Igel RX, water content 77%, orange tint density 40%), whereas CTRLs wore the regular contact lenses.
Each participant underwent an ophthalmologic examination to exclude, other than myopia, sight problems and were under ophthalmologist care throughout the whole experiment.
Participants were assigned to groups as a result of drawing lots. In one round of experiment (lasting 6 weeks), we could collect data from a maximum of 10 subjects. Due to the low number of people applying for participation in the study and our inclusion/exclusion criteria we usually did not have more than 8/10 volunteers per round. We always tried to have even number of participants per round to match the photoperiod for each group.
Primary outcome measure
Measured at baseline and 6-weeks:
1. Brain activations involved in cognitive task - that is performance and neuronal activity for two cognitive tasks measured using fMRI
2. Brain activations involved in emotional task - neuronal activity measured using fMRI during presentation of emotionally positive and negative stimuli
3. Performance in cognitive tasks directed to measure alertness, working memory and visuo-spatial memory.
Secondary outcome measures
Measured at baseline and 6-weeks:
1. Sleep quality measurement - assessed with subjective sleep quality questionnaires (PSQI - Pittsburgh Sleep Quality Index and ESS - Epworth Sleepiness Scale ) in different experimental conditions;
2. Circadian rhythm measurement - assessed with diurnal salivary cortisol pattern (morning and evening levels) and DLMO (dim light melatonin onset, five samples taken each session);
3. Sleep-wake cycle assessed with the use of actigraphs;
4. Emotional functioning - assessed with mood questionnaires (positive and negative affectivity and hedonic tone). Questionnaires used: PANAS - Positive and Negative Affect Schedule and SHAPS - Snaith-Hamilton Pleasure Scale.
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Age: 20-35 years old
2. Handedness: right
3. Regular sleep-wake cycle and sleep time between 6 and 9 hours per night
4. Experience in contact lens wearing (especially monthly disposable contact lenses without necessity to remove them for night)
5. Low level of daytime sleepiness, good sleep quality and non-extreme chronotype (on the basis of questionnaires).
Target number of participants
30 +30 in control group
Participant exclusion criteria
1. Any MR exclusion criteria (metal parts in the body, pacemaker, etc.)
3. Chronic diseases (eg diabetes), neurological and psychiatric conditions.
4. Other than myopia eye conditions.
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Malopolska Centre of Biotechnology
Narodowe Centrum Nauki
National Science Centre, NCN
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Planned publication in a high-impact peer-reviewed journal by 2020.
IPD sharing statement:
The datasets generated during and/or analysed during the current study will be stored in a publically available repository
Neuroimaging data will be available in the OpenFMRI repository (https://openfmri.org) in the time of results publication. Other data (questionnaires, biochemical) will be available upon request from the authors of the publication. All the data will be anonymised.
Intention to publish date
Participant level data
Stored in repository
Basic results (scientific)
2019 results in: https://www.biorxiv.org/content/10.1101/581314v1 (added 04/04/2019, not peer reviewed)