Purchase this article with an account.
F.J. Rucker, F. Adeusi, J. Wallman; Evidence for a Chromatic Component to Lens Compensation in Chicks . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1136.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Chick eyes compensate for defocus imposed by spectacle lenses by changes in eye length and choroidal thickness. Color signals from longitudinal chromatic aberration (LCA) could signal the sign of defocus, but previous studies have shown normal lens compensation under monochromatic light (Rohrer et al., 1992; Wildsoet et al., 1993).
Chicks wore plus or minus 6 or 8 D lenses on one eye for 3 days, under either blue (460nm) or red (620nm) light at 1.0 or 0.5 "lux" (corrected for chick photopic sensitivity); or white light at 0.5 or 0.2 "lux," conditions chosen to differentially stimulate the S and UV cones versus the L and double cones.
As our predecessors found, refractive error and vitreous chamber depth compensated for plus and minus defocus in white light and both monochromatic lights. However, the two components of lens compensation reveal a different story. Negative lenses: Unlike white light, which caused an increase in ocular length and a decrease in choroidal thickness (relative to the fellow control eye), our blue lights caused only an increase in ocular length (bright: 7 of 7 eyes increased; dim: 7 of 10 eyes increased; overall mean, 59 µm increase) with no change in choroidal thickness (bright: 4 of 7 decreased; dim: 4 of 10 decreased, overall mean, 3 µm decrease). Conversely, our red lights caused only a decrease in choroid thickness (7 of 8 decreased in both bright and dim; overall mean, 53 µm decrease), with no increase in ocular length (bright: 4 of 8 decreased; dim: 5 of 8 decreased; overall mean, 14 µm decrease). Thus, red and blue light has significantly different effects on both choroid and ocular length (p≤0.01, t–test). Positive lenses: Like white light, both our bright red and blue lights caused an increase in choroid thickness and a decrease in ocular elongation (relative to the fellow control eye); under the dim blue light, however, the choroid did not expand (8 of 17 decreased; mean, 2 µm increase, compared to 99 µm increase in dim red). Overall, choroidal expansion was significantly less under blue light (p<0.001).
The reduced lens compensation for choroid and eye–length under monochromatic illumination suggests that LCA may provide a signal of the sign of defocus for emmetropization. The differential effects on red and blue light on these two responses suggests that they are driven by different proportions of the cone–types, as has been shown for several behaviors in insects and humans.
This PDF is available to Subscribers Only