Delayed melatonin circadian timing, lower melatonin output, and sleep disruptions in myopic, or short-sighted, children

Study Objectives: This study investigated the differences in melatonin circadian timing and output, sleep characteristics, and cognitive function in myopic and non-myopic (or emmetropic) children, aged 8-15 years.Methods: Twenty-six myopes (refractive error [mean +/- standard error mean] -2.06 +/- 0.23 diopters) and 19 emmetropes (-0.06 +/- 0.04 diopters), aged 11.74 +/- 2.31 years were recruited. Circadian timing was assessed using salivary dim-light melatonin onset (DLMO), collected half-hourly for 7 hours, beginning 5 hours before and finishing 2 hours after individual average sleep onset in a sleep laboratory. Nocturnal melatonin output was assessed via aMT6s levels from urine voids collected from 05:30 pm to 8:00 am the following morning. Actigraphy-derived objective sleep timing were acquired for a week prior to the sleep laboratory visit. Cognitive assessments of sustained attention (using psychomotor vigilance task [PVT]) and working memory (using digit spans) were performed on the night of sleep laboratory.Results: Myopic children (9:07 pm +/- 14 minutes) exhibited a DLMO phase-delay of 1 hour 8 minutes compared to emmetropes (7:59 pm +/- 13 minutes), p = 0.002. aMT6s melatonin levels were significantly lower among myopes (18.70 +/- 2.38) than emmetropes (32.35 +/- 6.93, p = 0.001). Myopes also exhibited significantly delayed sleep onset, delayed wake-up time, poor and reduced sleep, and more evening-type diurnal preference than emmetropes (all p < 0.05). Finally, myopes showed a slower reaction time in the PVT (p < 0.05), but not digit span tasks at night.Conclusions: These findings suggest a potential association between circadian rhythm dysfunction and myopia in children.