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Frances J Rucker, Falk Schroedl; The Effects of Optic Nerve Sections on the Color and Luminance Emmetropization Mechanisms. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5521.
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© ARVO (1962-2015); The Authors (2016-present)
Visual signals are transmitted to the lateral geniculate nucleus through luminance and color sensitive neural pathways. It has been shown that these visual signals affect the process of emmetropization: changes in color make the eye more myopic, while changes in luminance make the eye more hyperopic. The aim of this experiment is to determine whether central processing is necessary for either or both of these emmetropization signals.
One to two week old, white leghorn chicks, underwent unilateral optic nerve lesion (n=15). Animals were allowed to recover for one week and ocular components (Lenstar LS900) and refraction (Hartinger Refractometer) were measured. The effect of the lesion was seen in the difference between the experimental eyes (X) and contralateral fellow eyes that served as controls (N). Chicks were then placed in cages illuminated with sinusoidally modulated light (2 Hz: 80% contrast) that changed in luminance contrast (LUM: n= 8) or color contrast (COLOR: n=7; red to green, mean illumination 680 lux). Animals were kept in these illumination conditions for three days (9am-5pm) and otherwise in the dark. Measurements were repeated. The effect of the illuminants was seen in the relative change between pre- and post-measures (ΔX- ΔN).
Effect of ONX Lesion :As seen in earlier experiments ONX produced relative hyperopia (3.23 ± 0.62D; p<0.001), with a reduction in eye length (117 ± 55 µm; P<0.05) and vitreous chamber depth (170 ± 64 µm; p<0.05) with lens thinning (-80 ± 25 µm; P<0.01) and choroidal thickening (111 ± 21 µm; p<0.001).Effect of Flicker Exposure:LUM exposure enhanced the effects of ONX with a further hyperopic shift (2.31 ± 0.7 D; p<0.01), a small reduction in eye length (-37 ± 43 µm) and vitreous chamber depth (-50 ± 57 µm), with lens thinning (-72 ± 48 µm) and an increase in anterior chamber depth (62 ± 33 µm).COLOR exposure with ONX had no effect on refraction and produced little change in eye growth compared to the contralateral eye, but increased choroidal thinning (-91 ± 16 µm; p<0.001) and vitreous chamber depth (98 ± 42 µm; p<0.05).
The results provide evidence for some central control of emmetropization, with an enhanced hyperopic shift associated with the luminance emmetropization response, and enhanced vitreal elongation associated with the color response. Retinal sources and signals involved need to be uncovered in upcoming studies.
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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