Sleep in infants does not influence future myopia development
Duration and quality of sleep in infancy exert no effect on the risk of developing refractive error at 3 years, according to a Singapore study.
Data from Brief Infant Sleep Questionnaire (BISQ) and cycloplegic autorefraction and axial eye length measurements revealed that total sleep duration (p=0.61) and number of night wakings (p=0.24) at 12 months were not associated with myopia (defined as spherical equivalent [SE] less than −0.5 dioptres) at 3 years (p>0.05). [Asia Pac J Ophthalmol 2018;doi:10.22608/APO.201739]
Likewise, each 1-hour increase in total sleep duration (p=0.07) and one-episode increase in the number of night wakings (p=0.49) were not related to axial length, the primary determinant of nonsyndromic myopia, at 3 years.
In tertile-based analysis, number of night wakings in tertiles 2 (1–2) and 3 (≥2) vs tertile 1 (<1) showed no association with axial length (p=0.53 for trend). On the other hand, there was a correlation observed between the tertile 3 (≥12.5 hours; p=0.006), but not tertile 2 (11–12.5 hours; p=0.11), of total sleep duration and longer axial length. Results for SE were null.
“We postulate that the relationship between sleep duration and axial length could be nonlinear with a certain threshold. However, we could not conclude that sleep duration was associated with myopia, as there was no association with SE either in the continuous or categorical analysis,” the authors noted.
The analysis included 376 children of Chinese, Malay and Indian ethnicity from The Growing Up in Singapore Towards Healthy Outcomes (GUSTO) birth cohort. At 12 months, infants slept an average of 8.9 hours at night, 2.9 hours during the day and 11.7 hours in total. On average, the number of night wakings per night was 1.5 in the Chinese group, 1.5 in the Malay group and 1.7 in the Indian group.
Infants with total sleep duration that exceeded the optimal total sleep duration (14 hours; n=325) had similar SE as those with total sleep duration <14 hours (n=51; p=0.30).
At 24 months, average screen time was 0.54 hours per day, whereas total near work time was 1.56 hours and outdoor time was 1.53 hours. Screen time was associated with neither SE (p=0.14) nor axial length (p=0.26).
Biological mechanisms by which sleep could promote the development of refractive error include the activation of the dopaminergic pathway and the damage of intrinsically photosensitive retinal ganglion cells (ipRGCs). Sleep deprivation downregulates dopamine D2R in ventral striatumin in humans, reducing activation of retinal dopaminergic pathways and leading to axial elongation. [J Neurosci 2012;32:6711-6717]
Findings of the present study show no association between sleep in infancy and the risk of developing myopia at 3 years, in contrast to previous studies reporting shorter sleep to be associated with myopia in schoolchildren.
The authors pointed out that the difference in sleep duration between 12 months and 3 years of age could be a possible confounder, as sleep at 12 months might still not be completely organized and hence more variable. Data obtained during this period might not be reflective of the sleep quality and quantity that would be achieved slightly later in infancy.
“In the current study, data on myopia was available only at 3 years,” they said. “Further large prospective cohorts with myopia data at two time points up to 6 years old and higher follow-up rates using objective sleep measures are needed.”