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Stephanie Britton, Molly Fellows, Frances Rucker; Temporal Frequency Sensitivity of the Emmetropization Mechanism in Chicks to Color and Luminance Flicker without Blue Light. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5178.
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Chicks were used to investigate the temporal sensitivity of the emmetropization mechanisms to color and luminance flicker. Previous experiments showed that exposure to 2 Hz luminance flicker produced a hyperopic refractive shift associated with a decrease in eye length and choroidal thinning, which disappeared when the light source did not contain blue light. Color flicker caused a myopic refractive shift, towards emmetropia, associated with an increase in eye length and less choroidal thinning.
4-5 day old chicks were exposed daily for three days (9am to 5pm) to sinusoidal luminance (LUM) or color modulation (R/G) at 80% contrast, at one of six frequencies: 0, 0.2, 1, 2, 5, 10 Hz. Mean illumination was 680 lux. Chicks were kept in the dark overnight. LUM was created with in-phase modulation and R/G with counter-phase modulation of red (615 nm) and green (515 nm) light. 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.
LUM: With exposure to luminance flicker, there were changes in refraction and eye length with temporal frequency. There was a pronounced hyperopic shift in refraction at 5 Hz (1.38 D) and 10 Hz (1.34 D), but not at ≤2 Hz (2 Hz: -0.66 D; 0.2 Hz: -0.48 D; Both p=0.03). The hyperopic shift in refraction at 10 Hz was associated with a 191 μm increase in eye length compared to a 354 μm increase in eye length at 0.2 Hz; p=0.004). Choroids thinned (range: -43 μm to -82 μm), but there was no significant change with frequency. R/G: With exposure to color flicker, there were changes in choroidal thickness with temporal frequency. There was less choroidal thinning at 0.2 Hz (-44 μm) than at 5 Hz (-82 μm; p=0.02). There was no significant variation in eye length (range: 209-298 um) or refractive error (± 0.50 D) with temporal frequency. NF: With no flicker there was a 0.1 D change in refraction associated with 346 ± 48 μm increase in eye length and 38 ± 12 μm choroidal thinning.
The emmetropization mechanism shows a temporal sensitivity to changes in color and luminance contrast that differentially affect choroidal thickness and eye length. Without blue light, higher temporal frequencies are necessary to produce the hyperopic shift seen with luminance flicker.
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