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Sigrid Diether, Florian Gekeler, Frank Schaeffel; Changes in Contrast Sensitivity Induced by Defocus and Their Possible Relations to Emmetropization in the Chicken. Invest. Ophthalmol. Vis. Sci. 2001;42(12):3072-3079.
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purpose. To test whether the level of contrast adaptation (CA) relates to
refractive development in the chicken. (CA refers to a spatial
frequency-selective increase of suprathreshold contrast sensitivity
after exposure to low-contrast patterns).
methods. CA was determined in individual chicks by comparing their optomotor
gain in response to drifting low-contrast stripe patterns before and
after treatment with spectacle lenses. The amount of CA was compared
with the loss of contrast predicted from defocus at the tested spatial
frequency. The reversion of CA and recovery from deprivation myopia
were studied while the retinal image features were controlled by
forcing the animals to watch spatially filtered digital video clips.
results. CA was induced by wearing positive and negative lenses for 1.5 hours,
both without and with cycloplegia, but was less pronounced in the case
of positive lenses when accommodation was intact. The amount of CA at a
tested spatial frequency was predicted from the loss of contrast
calculated from the modulation transfer function for a defocused
optical system. Watching low-pass–filtered video clips induced
deprivation myopia and inhibited recovery from it. It also prevented
the reversal of CA that was previously induced by deprivation. Both
recovery from deprivation myopia and recovery from CA occurred with
sharp video clips, although less so than with normal visual exposure.
conclusions. CA changes with retinal image sharpness and occurs even when
accommodation is intact. Because CA correlates with myopia induced by
frosted occluders, negative lenses, and low-pass–filtered video clips,
and its reversal correlates with recovery from myopia, it is possible
that shifts in CA may represent a signal related to refractive
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