Ingrid Koumbo, PhD Candidate
The mechanisms underlying the onset and progression of myopia are complex and involve many factors. The rapid increase in the prevalence of myopia requires further research and understanding of factors that affect its onset and progression. This study investigated the differences in the timing of the melatonin circadian rhythm (DLMO timing), total melatonin output, and sleep outcomes between myopic and emmetropic young adults.
Myopes showed a delayed melatonin circadian timing (of 1 hour 12 minutes) as measured by DLMO, lower melatonin secretion (difference of 13.34) as measured by urinary aMT6s levels compared with emmetropes. In addition, the sleep profile of myopes revealed a delayed sleep timing (delayed sleep onset time, greater sleep onset latency and shorter sleep duration, and a more evening-type diurnal preference).
This study suggests that young adult myopes have significantly delayed circadian timing compared with emmetropes, indicating the importance of sleep and melatonin rhythms in the pathogenesis of myopia.
Myopia, or near-sightedness, is associated with delayed melatonin circadian timing and lower melatonin output in young adult humans
Ranjay Chakraborty, Gorica Micic, Lisa Thorley, Taylah R Nissen, Nicole Lovato, Michael J Collins, Leon C Lack.
Study Objectives: Myopia is the most common refractive vision disorder and predisposes the eye to many blinding conditions in adulthood. Recent research has suggested that myopia is associated with increased endogenous melatonin production. Here we investigated the differences in melatonin circadian timing and output in young adult myopes and non-myopes (or emmetropes) as a pathogenesis for myopia.
Methods: A total of 18 myopic (refractive error [mean ± standard deviation] −4.89 ± 2.16 diopters) and 14 emmetropic participants (−0.09 ± 0.13 diopters), aged 22.06 ± 2.35 years were recruited. Circadian timing was assessed using salivary dim light melatonin onset (DLMO), collected half-hourly for seven hours, beginning five hours before and finishing two hours after individual average sleep onset in a sleep laboratory. Total melatonin production was assessed via aMT6s levels from urine voids collected from 06:00 pm and until wake-up time the following morning. Objective measures of sleep timing were acquired a week prior to the sleep laboratory visit using an actigraphy device.
Results: Myopes (22:19 ± 1.8 h) exhibited a DLMO phase-delay of one hour 12 minutes compared with emmetropes (21:07 ± 1.4 h), p = 0.026, d = 0.73. Urinary aMT6s melatonin levels were significantly lower among myopes (29.17 ± 18.67) than emmetropes (42.51 ± 23.97, p = 0.04, d = 0.63). Myopes also had a significant delay in sleep onset, greater sleep onset latency, shorter sleep duration, and more evening-type diurnal preference than emmetropes (all p < 0.05).
Conclusion: These findings suggest a potential association between circadian rhythms and myopia in humans.
Chakraborty, R., Micic, G., Thorley, L., Nissen, T.R., Lovato, N., Collins, M.J., Lack, L.C. (2020) Myopia, or near-sightedness, is associated with delayed melatonin circadian timing and lower melatonin output in young adult humans, Sleep. [online]