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Frances J Rucker, Christopher Patrick Taylor; Short-wavelength cone contrast reverses the sign of defocus for emmetropization in chick. Invest. Ophthalmol. Vis. Sci. 2018;59(9):679.
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© ARVO (1962-2015); The Authors (2016-present)
Chicks respond to wavelength defocus produced by longitudinal chromatic aberration (LCA) with more growth in red monochromatic light than blue monochromatic light. They also respond to a chromatic signal from LCA that predicts reduced growth when red contrast>blue contrast, and increased growth when blue contrast>red contrast. The goal of this experiment was to determine whether contrast, temporal frequency, or blue light content determines which of these signals takes precedence.
457 chicks viewed temporal stimuli for three days on an 8/16 hour light/dark cycle. Sinusoidal temporal stimuli (0.2 and 10 Hz) were presented at low (vector length: 30%) and high contrast (vector length: 80%), with seven different cone contrast ratios represented in polar coordinates (0°, 22.5°, 45°, 67.5°, 90°, 120°, 145°; Mean: 650 lux). “White+B” represents white stimuli with long-, middle- and short-wavelength sensitive cone contrast (LM-cone and S-cone). S-cone contrast increased from zero at 0° to a maximum at 90° and vice versa for LM-cone contrast. “White –B”, represents white stimuli (with blue light) but only L- and M-cone contrast. Measurements of the change in ocular components were made with a Lenstar LS 900 and a Hartinger refractometer. The major/ minor axes of the resulting data ellipse were calculated. A difference in axis length indicates sensitivity to relative cone contrast, while ellipse orientation indicates whether detection was of wavelength defocus or a chromatic signal.
Vitreous chamber growth in low contrast conditions showed sensitivity to relative cone contrast, and was dependent on stimulus orientation, a frequency of 0.2 Hz, and blue light content (F = 3.889; p = 0.002).With 30% contrast, at 0.2 Hz, in “White +B”, the vitreous changes resulted in a data ellipse, with axes dimensions of 202 and 175 µm, orientated at 135.04°, indicating detection of a signed chromatic signal.With 30% contrast, at 0.2 Hz, in “White –B”, the vitreous changes resulted in a data ellipse, with axes dimensions of 254 and 172 µm, orientated at 42.31°, indicating detection of a signed wavelength defocus signal.
Myopia development depends on whether the eye responds to the sign of wavelength defocus or a chromatic signal from LCA, this in turn depends on the presence or absence of a blue light component, low temporal contrast, and low temporal frequency exposure.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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