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C.-S. Kee, L. Deng, W.-C. Ho; Time Course of Changes in Astigmatic Components in Chicks With Myopia Induced by Form-Deprivation or Lens-Wear. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3716.
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Astigmatism is frequently associated with myopic eye growth in both clinical and experimental eye studies. However, when astigmatism is present, the time course for individual principal powered meridians during myopic eye growth is unclear. This study characterized the developmental changes of the individual principal powered meridians in chicks with experimentally induced myopia.
White Leghorn chicks wore -10 D lenses (n=10) or diffusers (n=10) from day 5 for 2 weeks. An age-matched group without any treatment served as a control group (n=9). After the initial measurement performed on day 5, measurements were made frequently throughout the 2-wk treatment period (days 6-19 except days 10, 11, 17 &18). Refractive errors were measured using a modified Hartinger's refractometer as previously described. Longitudinal changes of each refractive component (spherical-equivalent refractive error, SE; cylinder, Cyl; J0 & J45; most hyperopic meridian, MHM; most myopic meridian, MMM) were fit with the function: a+b*log(Age).
Compared to control birds, birds treated with -10D lenses or diffusers exhibited significantly more rapid changes with age on all the refractive components tested (p≤0.001). The diffuser-wearing eyes showed significantly more rapid changes in SE, MHM and MMM than did the eyes wearing -10D lenses over the two weeks treatment period. In both treatment groups, the MMM component changed more rapidly than did the MHM (both p<0.001). However, the slopes for Cyl, J0 and J45 were not significantly different between the two treatment groups over the two weeks treatment period.
Hyperopic defocus and form deprivation result in both myopia and astigmatism. Although the two experimentally induced myopias progressed at different rates, the similarities in the characteristics of astigmatic components suggest that they share (or are limited by) common anatomical structures.
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