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M. L. Kisilak, E. L. Irving, M. C. W. Campbell; Once Optical Blur Exceeds a Threshold Value During Normal Growth in Chick Eyes, It Reduces With Growth. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1616.
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© ARVO (1962-2015); The Authors (2016-present)
We wish to understand longitudinal changes in ocular image quality during normal growth and in eyes with lens-induced refractive errors. We have shown that optical blur from astigmatism and aberrations decreases in normal eyes with growth and that optical properties (in addition to spherical refraction) differ between normal and goggled eyes. These previous results are suggestive of visual feedback. Here we consider optical blur in a larger number of control eyes and eyes goggled with differing lens powers.
On the first day post-hatching, chicks were unilaterally fitted with -30D, -15D or +10D goggles. The other eye acted as a control. Another set of birds were also obtained and allowed to develop naturally. On several days, goggles (if worn) were removed for brief periods of time for Hartmann-Shack wavefront measurements. Hartmann-Shack images were analyzed for the largest common pupil size within a set of birds on a given day. Equivalent blur was used to estimate the angular blur on the retina.
Spherical refractive errors of goggled eyes, control eyes and control birds emmetropized as expected. Equivalent blur due to either higher-order aberrations (HOA) or astigmatism in control eyes had a large variation on day 0 that decreased with growth. Equivalent blur due to HOA decreased in control birds from day 4 onwards. It appears that, above a similar minimum value of equivalent blur, the blurs due to both HOA and astigmatism reduce. This threshold value decreased linearly with age for both types of blur. Only control eyes of birds goggled with -15D lenses showed a correlation between equivalent blurs due to HOA and astigmatism. Goggling either increased the threshold at which blur reduced or interfered with the above-threshold decrease. For example, equivalent blur due to astigmatism did not reduce in any of the goggled eyes. Results for +10D goggles were equivocal, presumably because the blur failed to reach threshold values. Only -30D goggled eyes showed a significant correlation between equivalent blurs due to HOA and astigmatism.
There appears to be an age dependent threshold value of blur below which the blur continues to increase. Above this value, blurs then reduce with age in control eyes along with the age-dependent threshold value. Goggling interferes with this decrease.
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