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John R. Phillips, Mohammad Khalaj, Neville A. McBrien; Induced Myopia Associated with Increased Scleral Creep in Chick and Tree Shrew Eyes. Invest. Ophthalmol. Vis. Sci. 2000;41(8):2028-2034.
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purpose. To investigate the role of scleral creep in the axial elongation of
chick and tree shrew eyes with induced myopia.
methods. Form-deprivation myopia was induced with a diffusing occluder worn over
one eye. Scleral samples from the posterior pole and equatorial regions
of myopic, contralateral (control), and age-matched normal chick and
tree shrew eyes were loaded in vitro with a force of 5 g for 20
minutes while creep extension was monitored. The elastic behavior of
sclera from myopic, control, and normal chick eyes was also compared.
results. In both chick and tree shrew, posterior and equatorial scleral samples
from myopic eyes had significantly (P < 0.05) greater
creep extensions than equivalent samples from control and normal eyes
(n = 10, each group). Among individual tree shrews the
difference in creep rate between the sample from the myopic eye and
that from the control eye correlated with vitreous chamber elongation
(r = 0.746, P < 0.05) and development of
myopia (r = 0.792, P < 0.01) in the
deprived eye. No such association was found in the data from chicks.
The elastic properties of chick sclera were unaffected in
conclusions. In chick and tree shrew, form-deprivation myopia is associated with
increased creep rate of posterior and equatorial sclera. In tree shrew,
the correlation between increased scleral creep rate and vitreous
chamber elongation in myopic eyes supports the hypothesis that induced
changes in the axial length of the mammalian eye are mediated by
changes in the creep properties of the sclera.
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