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Jonathan Elin-Calcador, Shanta Sarfare, Christopher Taylor, Frances J Rucker, Debora L Nickla; Blue light in the evening stimulates ocular growth and alters ocular rhythms in chicks. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3154.
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© ARVO (1962-2015); The Authors (2016-present)
Recent evidence has shown that moderate levels of blue light are sufficient to suppress the nighttime rise in serum melatonin in humans, suggesting that luminous screens may be deleterious to sleep cycles and to other functions. Little is known however, about effects on ocular physiologies. We used the chick model to ask whether blue light exposure at the end of the light cycle affected ocular growth rates, and/or altered the parameters of the rhythms in axial length or choroidal thickness.
10-day-old chicks were exposed daily to 4 hours blue light (460 nm) at the end of the (white) light cycle (total=12L/12D) for 9 days. Two intensities were used: “mid” (equi-radiant to white: 201 lux, n=16) and “bright” (equi-luminant to white: 575 lux, n=8). “Bright” 2-hr exposures were also tested (n=8). A third group was exposed to yellow evening light (637 lux, n=8). Controls remained in white light for the full 12 hours of the light cycle (588 lux; n=23). Changes in ocular dimensions were measured by A-scan ultrasonography. On day 9, measurements were made at 6-hour intervals over 24 hours starting at noon to assess rhythms. Subgroups of “mid blue”, “bright blue” and “white” were also measured at 14 and 21 days.
4 hours of “mid” blue light in the evening stimulated ocular growth relative to that of white controls (839 µm vs 766 µm/9d; p=0.015). The effect lasted for up to 14 days (p=0.01). In the “bright” condition, the growth effect was enhanced (915 µm vs 839 µm/9d; p<0.01), the duration of effect was extended (X vs C at 21d: p<0.0001), and 2 hours was sufficient to cause the growth stimulation (898 µm vs 766 µm; p<0.05). Eye growth in “yellow” did not differ from controls. “Mid” blue light resulted in a significant phase-advance in the axial length rhythm (acrophase: 13:35 vs 17:40; p<0.001), a phase-delay in the choroidal thickness rhythm (3:00 vs 00:25; p<0.05), and a larger choroidal rhythm amplitude relative to controls (71 µm vs 47 µm; p<0.05).
Exposure to blue light in the evening alters the ocular rhythms involved in eye growth regulation in chicks, and increases ocular growth rate. These findings suggest that prolonged use of blue-emitting devices in the evening may have deleterious effects on these same ocular rhythms in children, with potential consequences on eye growth.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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