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Debora L Nickla, Kristen Totonelly; Brief light exposure at night disrupts the circadian rhythms in eye growth and choroidal thickness in chicks. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5529.
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© ARVO (1962-2015); The Authors (2016-present)
Changes in eye growth that lead to myopia or hyperopia are associated with alterations in the circadian rhythms in eye length and choroidal thickness in animal models. Recent studies have shown that light at night has deleterious effects on human health via “circadian disruptions” in various physiological rhythms. The purpose of this study was to determine the effects of 2-hour episodes of light at night on the rhythms in axial length and choroidal thickness, and on growth rate and refraction in the chick model.
At 2 weeks of age, birds received light (700 lux) between 12:00 am and 2:00 am for 7 days (n=18; total light=14 hr). Age-matched controls had a continuous dark night (n=22; 14L/10D). Ocular dimensions were measured using high-frequency A-scan ultrasonography on the first day, and again on day 7 at 6-hr intervals for 24 hr, starting at noon. Measurements during the night used a photographic safe-light. These data were used to determine rhythm parameters of phase and amplitude. Other experimental and control groups were measured at various intervals over the course of 4 weeks to track growth rates. Refractive errors were measured in 12 birds.
Eyes of birds in a normal L/D cycle showed sinusoidal 24-hr period rhythms in axial length and choroid thickness, as expected (Nickla et al., 1998). Light at night altered both the rhythms in axial length and choroidal thickness, such that neither could be fit to a 24-hr sine function. Light caused an acute, transient stimulation in ocular growth in the 6-hr period from 12 am-6 am (X vs C: 37 µm vs 5 µm; p=0.037). This may be responsible for the increased growth rate 4 weeks later (827 µm vs 703 µm/7 d; p<0.0001), and the more myopic refraction (0.8 vs 1.8 D; p=0.03). ANOVA showed that time-of-day accounted for the differences in the changes in axial length between experimental and controls (F3,108=4.31; p=0.0065). Light at night also abolished the rhythm in choroidal thickness; time-of-day accounted for the differences in choroidal thickness changes between experimental and controls (ANOVA, F3,123=7.17; p=0.00018).
Brief light at night alters the rhythms in axial length and choroidal thickness in chicks, and eventually results in an increase in ocular growth rate. We speculate that these circadian disruptions lead to the development of ametropias.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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