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J. Wallman, X. Zhu, F. J. Rucker; Can Eyes Shrink?. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3929.
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It seems more natural that eyes or animals should grow than shrink. However, given that tissues are continuously remodeled under homeostatic control, why should shrinkage be more implausible than growth? We demonstrate that chick eyes can shrink when wearing positive lenses.
Chicks wore +6, +7, or +10 D lenses over one eye for 3 days. Ocular length (cornea to sclera) was measured by ultrasound biometry at the beginning and the end of each experiment. To estimate measurement error, we reviewed data from experiments in which chicks were measured at intervals of up to 2 hr, during which they wore various lenses. The standard deviation of these measurements overestimated the measurement error because it was based on a heterogeneous sample of experimental animals measured at different times of day.
Wearing positive lenses for 3 days reduced ocular elongation by two-thirds, including a quarter of the eyes in which the ocular length became shorter than before (see histogram). The mean change in ocular length was 58 µm [s.d.=96 µm], compared to 184 µm in the untreated fellow eyes. Other chick eyes, measured twice in 2 hr or less, had a standard deviation of 31 µm (see superimposed histogram, scale on right axis, shifted to match mean of main histogram). From these distributions, we can infer that measurement error would account for 5 of the 202 positive-lens-wearing eyes becoming shorter, rather than the 56 eyes that we encountered.
Chick eyes can shrink when wearing positive lenses, facilitating compensation for the imposed myopia.
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