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Christopher Taylor, Greg Lin, Nathaniel Watts, Frances J Rucker; Species differences in emmetropization under monochromatic light rearing. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3160.
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© ARVO (1962-2015); The Authors (2016-present)
Experiments that have reared animals under restricted wavelength conditions have disagreed on the effect of wavelength on emmetropization. Possible sources of the disagreement among experiments are the lights/species used, prior visual experience, restriction duration, or effects of circadian rhythms. Exp. 1 followed methods of Gawne et al. (2017) in tree shrew, in the chick, to compare across species. Bird activity was monitored to assess the indirect influence of circadian rhythms. Exp. 2 tested whether depriving chicks of any broadband light experience from birth would alter emmetropization as in Foulds et al (2013). Exp.3 extended the duration of exposure of Exp. 2.
Exp. 1: 33 birds experienced brooder lighting until 7 days-old and then were exposed to either steady or pseudo-randomly flicking light (mean=424 lux) that was monochromatic red (640±10 nm), blue (460±10 nm), or white light for 10 days on a 12h/12h light/dark cycle. Ocular biometry (Lenstar LS 900) and Refractive Error (IR PhotoRefractor) was measured every two days during the 10 days. Bird activity in the cages was measured via a camera with a motion detection from day 4 through 10 of exposure. In each of Exp. 2 and 3: 16 newly hatched birds were placed under red or blue steady illumination that matched Exp. 1. Biometry and refraction were measured on day 10 and 17 in Exp.2 and on days 9, 20, 30 and 38 in Exp. 3.
Exp 1: both light color and flicker affected axial elongation (p=0.001; p=0.02) and vitreous chamber depth (p < 0.001; p = 0.02). Red/white light increased the eye growth rate compared to blue light, while flicker reduced eye growth. No differences in refractive error were found. Activity was greater under red than either white/blue light (p < 0.001). Exp. 2 and 3 did not show an increased rate of axial elongation and vitreous chamber depth in red/blue lighting conditions (p=0.62). Choroids thickened in red light (p < 0.001 both), which affected refraction at 9 days (p=0.02).
Monochromatic light guides emmetropization via wavelength defocus in the chick.Differences in activity among the conditions suggests that a wavelength restricted illuminant influences circadian rhythms. Restricted visual experience from birth alters the emmetropization response to wavelength defocus. In sum, previously found species differences in emmetropization may be the result of circadian influences and/or developmental effects.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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