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Title: Early astigmatism can alter myopia development in chickens
Authors: Vyas, SA 
Kee, CS 
Issue Date: Feb-2021
Source: Investigative ophthalmology and visual science, Feb. 2021, v.62, no. 2, 27, p. 1-16
Abstract: Purpose: To determine the effects of optically imposed astigmatism on myopia development in chickens.
Methods: Chicks were randomly assigned to wear either spherical (−10D, “LIM”, n = 14) or sphero-cylindrical lenses (n ≥ 19 in each group) monocularly for a week from 5 days of age. All lenses imposed the same magnitude of spherical-equivalent hyperopic defocus (−10D), with the two astigmatic magnitudes (−8D or −4D) and four axes (45°, 90°, 135°, or 180°) altered to simulate four subtypes of clinical astigmatism. At the end of the treatment, refractive state was measured for all birds, whereas ocular axial dimensions and corneal curvature were measured for subsets of birds.
Results: Sphero-cylindrical lens wear produced significant impacts on nearly all refractive parameters (P < 0.001), resulting in myopic-astigmatic errors in the treated eyes. Compared to LIM, the presence of astigmatic blur induced lower myopic error (all except L180 group, P < 0.001) but with higher refractive astigmatism (all P < 0.001) in birds treated with sphero-cylindrical lenses. Distributions of the refractive, axial, and corneal shape parameters in the sphero-cylindrical lens-wear groups indicated that the astigmatic blur had directed the eye growth toward the least hyperopic image plane, with against-the-rule (ATR) and with-the-rule (WTR) astigmatisms typically inducing differential biometric changes.
Conclusions: The presence of early astigmatism predictably altered myopia development in chicks. Furthermore, the differential effects of WTR and ATR astigmatisms on anterior and posterior segment changes suggest that the eye growth mechanism is sensitive to the optical properties of astigmatism.
Keywords: Myopia development
Astigmatism
Chicken
Publisher: Association for Research in Vision and Ophthalmology
Journal: Investigative ophthalmology and visual science 
ISSN: 0146-0404
EISSN: 1552-5783
DOI: 10.1167/iovs.62.2.27
Rights: Copyright 2021 The Authors
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (https://creativecommons.org/licenses/by-nc-nd/4.0/).
The following publication Vyas, S. A., & Kee, C. S. (2021). Early astigmatism can alter myopia development in chickens. Investigative Ophthalmology & Visual Science, 62(2), 1-16 is available at https://doi.org/10.1167/iovs.62.2.27
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