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Stephanie Britton, Stephan Hanowsky, Frances J Rucker; Blue light protects against temporal frequency dependent refractive changes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3598. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
A previous experiment indicated that chicks exposed to luminance flicker without blue light showed a hyperopic shift at higher temporal frequencies and a myopic shift at lower frequencies. In this experiment we test the hypothesis that blue light is important in emmetropization by comparing the response of chicks to luminance flicker with and without blue light over a range of temporal frequencies.
4-5 day old White Leghorn chicks were exposed daily for three days (9am to 5pm) to sinusoidal luminance modulation at 80% contrast, at one of six temporal frequencies: 0, 0.2, 1, 2, 5, 10 Hz. Luminance flicker “without blue” light was created with in-phase modulation of red and green, while “with blue” flicker was created with in-phase modulation of red, green and blue light. Mean illumination was 680 lux. Chicks were maintained in a dark chamber overnight. Changes in ocular components were measured before and after the experiment with a non-contact ocular biometer (Lenstar LS 900), and refractive error was measured with a Hartinger Coincidence Refractometer. Photokeratometry was used to calculate corneal astigmatism and images were analyzed with Image J.
Refraction, eye length, and choroidal changes were dependent on temporal frequency (p<0.03 all) and on the interaction between frequency and blue light (p<0.03 all). Without blue, refractions were more hyperopic with higher temporal frequencies, and more myopic at lower temporal frequencies. There was a hyperopic shift (> 1 D) at 5 and 10 Hz, and a myopic shift (> -0.6 D) at ≤2 Hz, and an increase in astigmatism along J45 (p=0.04). With blue light, refraction remained constant (mean change -0.24 D). Without blue light, there was less eye growth at high frequencies and more at low frequencies. Eyes were 145 µm shorter at 10 Hz than they were at 0.2 Hz (p<0.003), while with blue, they were only 77 µm shorter. Without blue light, anterior chamber depths were deeper (p=0.006), while choroids were thinner at low and intermediate temporal frequencies, contributing to the myopic shift at low frequencies. At 5 Hz, choroids thinned 46 µm more without blue light, than with blue light (p=0.03).
Emmetropization shows a temporal, blue light sensitivity. Blue light protects against temporal frequency dependent refractive changes through modification of eye length, choroidal thickness, anterior chamber depth and corneal curvature.
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