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Y. Tian, C. Wildsoet; Diurnal Fluctuations of Ocular Dimensions and Aberrations in Growing Chick Eyes: Implication for Eye Growth Regulation . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2283.
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Purpose: To study the diurnal fluctuations of ocular dimensions and aberrations in normal and ciliary nerve sectioned (CNS) growing chick eyes. Methods: The ocular dimensions for both eyes of 5 CNS (right eyes only) and 4 normal chicks were measured with high frequency A–scan ultrasonography four times a day (at 9 am, 12 pm, 4 pm and 7 pm), on days 11, 14, 18, 21 and 32. The aberrations of the same eyes were measured using an aberrometer at the same time points on days 12, 15, 19, 22 and 33. Refractive errors and root mean square values (RMS) for higher order aberrations were derived from corresponding Zernike coefficients. ANOVA analyses were applied to right eye data to test treatment, age and diurnal effects (significance level p < 0.05). Results: Treatment effects(CNS vs. normal): CNS eyes were more hyperopic than normal eyes, consistent with CNS eyes having thinner lenses than normal eyes, and they also had more positive spherical aberration than normal eyes. Age effects: Astigmatism, RMS values for the combined 3rd and 4th order aberrations, coma, trefoil, and quatrefoil all decreased with development. Spherical aberration showed a positive shift with age in normal eyes, while there were no significant age–related changes in CNS eyes. Anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and thus optical axial length (OAL) all increased with development. Diurnal effects: Spherical equivalent refractive error (defocus), spherical aberration, ACD, VCD, OAL and choroidal thickness (CT) all showed significant diurnal fluctuations. Refractive errors were more hyperopic in the evening than in the morning, while spherical aberration was more negative in the evening. ACD, VCD and OAL were all longer in the evening than in the morning, while CT was thinner in the evening. Conclusions: Astigmatism and most 3rd and 4th order aberrations decreased during early ocular development. Significant diurnal variations in ocular dimensions and some aberrations were also observed. Interestingly, while axial length increased across the day (partly as a result of choroidal thinning), the eyes became more hyperopic over the same time frame. This apparent contradiction cannot be accounted for by changes in the optical length of any ocular component, thus implying diurnal changes in the curvature of one or more of the ocular surfaces. The diurnal fluctuations in refractive error and spherical aberration expose the retina to different magnitudes and/or types of blur across the day. These temporal changes may be used to decode the eye’s refractive error by the retina in ocular growth regulation.
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