Objectives: Insomnia is associated with neuropsychological dysfunction. Evidence points to the role of nocturnal light exposure in disrupted sleep patterns, particularly blue light emitted through smartphones and computers used before bedtime. This study aimed to test whether blocking nocturnal blue light improves neuropsychological function in individuals with insomnia symptoms.

Methods: This study used a randomized, placebo-controlled crossover design. Participants were randomly assigned to a 1-week intervention with amber lenses worn in wrap-around frames (to block blue light) or a 1-week intervention with clear lenses (control) and switched conditions after a 4-week washout period. Neuropsychological function was evaluated with tests from the NIH Toolbox Cognition Battery at three time points: (1) baseline (BL), (2) following the amber lenses intervention, and (3) following the clear lenses intervention. Within-subjects general linear models contrasted neuropsychological test performance following the amber lenses and clear lenses conditions with BL performance.

Results: Fourteen participants (mean(standard deviation, SD): age = 46.5(11.4)) with symptoms of insomnia completed the protocol. Compared with BL, individuals performed better on the List Sorting Working Memory task after the amber lenses intervention, but similarly after the clear lenses intervention (F = 5.16; p = .014; η2 = 0.301). A similar pattern emerged on the Pattern Comparison Processing Speed test (F = 7.65; p = 0.002; η2 = 0.370). Consideration of intellectual ability indicated that treatment with amber lenses "normalized" performance on each test from approximately 1 SD below expected performance to expected performance.

Conclusions: Using a randomized, placebo-controlled crossover design, we demonstrated improvement in processing speed and working memory with a nocturnal blue light blocking intervention among individuals with insomnia symptoms. (JINS, 2019, 25, 668-677).