The effects of long-term reduction of short wavelength light in humans.

INTERVENTION: 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 ph CONDITION: Participants were young, healthy volunteers. ; Not Applicable PRIMARY OUTCOME: ; 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.; 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). SECONDARY OUTCOME: ; 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.; ;