Purchase this article with an account.
David S. Hammond, Frank F. Yang, Christine F. Wildsoet; Longitudinal Chromatic Aberration Guides the Emmetropization Response of Young Chicks to Myopic Defocus under Reduced Illumination. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2831.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
In this study, we investigated whether chromatic aberration cues are used to guide emmetropization in chicks under low luminance conditions. Responses to imposed optical defocus were compared in young chicks reared under conditions in which these cues were present (either broad spectrum or dichromatic, involving the two ends of the visible spectrum) or removed (monochromatic).
32 young chicks were reared from 4 days of age with 4 different lighting conditions: 20 lux red (633nm); 20 lux UV (390nm); 10 lux red + 10 lux UV (dichromatic); broad spectrum bright White Light (4000 lux). LEDs were used for red & UV light as they have narrow bandwidths. The chick photopic sensitivity function was used to ensure equivalent luminances were used at 633 nm & 390nm. The left eye of each chick wore either a +10 or -10 D lens, with the fellow eye serving as a control. Biometric data were collected on days 0, 2, 4, and 7, with refractive error (RE) data, on days 0 and 7.
Under the 20 lux monochromatic conditions (UV or red), compensation to myopic defocus (+10 D) was disrupted, with eyes becoming myopic instead of hyperopic, and increasing their elongation rate relative to the fellow eye (RE: -5.20 D, UV; -11.25 D, red; optical axial length: 0.508 mm, UV; 0.521 mm, red). In contrast, under the dichromatic conditions, eyes showed hyperopic shifts in refraction and slowed axial elongation relative to their fellows (+ 5.13 D, -0.265mm). This response pattern is consistent with normal compensation and similar to that seen under the white light conditions (+8.5 D, -0.393 mm). The responses to the -10 D lenses were independent of the lighting conditions, with all groups showing similar myopic changes in refraction and increases in axial lengths.
Emmetropization to myopic defocus (+10 D) is compromised under low luminance (20 lux) monochromatic conditions (390nm or 633nm), but not under low luminance dichromatic conditions involving the ends of the visible spectrum (390nm + 633nm), which introduce significant chromatic aberration. These results imply that chromatic aberration cues provide critical information about the direction of defocus for emmetropization when luminance is low. Myopia appears to be the default response when illumination is low and cues are inadequate.
This PDF is available to Subscribers Only