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T. Mihashi, T. Li, J.R. Basarab, Y. Hirohara, H.C. Howland; Constant light produces more optical aberration especially overcorrected spherical aberrations in chickens . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4301.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Chickens grown in constant light exhibit flattened corneas, shallow anterior chambers and hyperopia (Li, Troilo, Glasser and Howland (1995) Vision Res). A question addressed here was whether the optical aberrations of chicken eyes are also affected by constant light conditions. Methods: Twelve eyes of six chicks in constant light conditions (CL) and ten eyes of five chicks in normal light conditions (normal) were measured for refraction and wavefront aberrations 28 days after hatching. Wavefront aberrations were measured using a Shack–Hartmann wavefront aberrometer. The alignment of the eye to the aberrometer was objectively checked using the first Purkinje reflex and images of the pupil of the eye. This mage of the anterior segment was grabbed simultaneously with the Hartmann image. Wavefront aberrations for a 3.5 mm pupil were obtained and analyzed using Zernike polynomials of which the coordinate origin was the center of the pupil. A line through the nasal corner of the eye to the center of the pupil was chosen to be horizontal axis. During measurements, chicks, without lid retractors, were held gently by the authors in order not to distort the cornea. Results: Higher–order aberrations of normal chicks (average ±SD; 0.250 ± 0.047µ) were smaller than those of CL chicks, which were 0.704±0.100 (P<0.001, t–test). Combined RMSs of the 3rd–,4th–, 5th–, and 6th–order wavefront aberrations in CL chicks were also statistically significantly larger than those in normal chicks. Only the Zernike coefficients of oblique astigmatism, 3rd order coma, and 4th order spherical aberration showed significant differences between CL and normal chicks. The average of 4th order spherical aberration in CL chicks was –0.522µ and that in normal chicks was –0.094µ. This overcorrected spherical aberration was due to either the smaller curvature of CL or to the more prolate surface than normal. Conclusions: Higher–order aberrations of normal chicks 28 days after hatching were larger than those of normal human eyes (0.250µ > 1.753/100 = 0.054µ). Astigmatism and higher–order aberrations were increased by CL conditions as expected from corneal flattening.
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