Bi-directional corneal accommodation in alert chicks with experimentally-induced astigmatism

Chu, Chin Hung Geoffrey; Zhou, Yongjin; Zheng, Yongping; Kee, Chea Su

doi:10.1016/j.visres.2014.03.002

Cited by 10 publications

(11 citation statements)

References 30 publications

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“…The ossicle numbers 1 (inferior) and number 9 (superior), “+” elements (on top of the others), are located nearly at the vertical meridian (i.e., the axis meridian); while the ossicle numbers 6 and 10, “-” elements (under the others), provide a buffer for the movement of the axis meridian. In combination with our previous findings of corneal accommodations [ 70 ], we speculated that the cornea could respond to imposed astigmatism, for example, the H90 group by contraction of the ciliary muscles ( i . e ., positive corneal accommodation), enhanced by the specific pattern of ossicles, to create an against-the-rule corneal profile (ossicles number 1&9 move forward, while number 6&10 move backward) for astigmatic compensation.…”

Section: Discussionsupporting

confidence: 64%

“…The reverse is the case; the cornea compensates for the imposed ATR astigmatism, the corneal curvatures are relatively flatter as a result of negative corneal accommodation. However, the magnitude of negative corneal accommodation is smaller than that of positive corneal accommodation [ 70 ] that may be due to the limitation of the ossicles, and/or the cornea structure. Excessive negative accommodation might stretch the cornea and sclera which become flatter, along the horizontal meridian in particular.…”

Section: Discussionmentioning

confidence: 99%

“…After measuring the refractive changes for a large number of astigmatism imposed chicks, a subset of birds (n = 8) randomly assigned to each group was used for corneal topography and eyeshape imaging. Corneal curvatures and astigmatism were measured using a custom-made videokeratography system in alert chicks (see [ 70 ] for details). The system captured Placido-ring images ( i .…”

Section: Methodsmentioning

confidence: 99%

“…e ., the first Purkinje image) in multiple-shot mode and analysed the central 2.80mm-diameter cornea using a custom MatLab algorithm (MatLab; The MathWorks, Natick, MA. In order to rule out the potential effect of accommodation on corneal curvature, only images acquired at relaxed accommodative status were used, these images were identified from 500–1500 Placido-ring images from each eye as demonstrating the most frequently observed mean corneal curvature [ 70 ]. The average values of the corneal curvatures along the two principal meridians were calculated, assuming a corneal refractive index of 1.369 [ 71 – 73 ], from three good images per eye at different time points.…”

Section: Methodsmentioning

confidence: 99%

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Effects of Optically Imposed Astigmatism on Early Eye Growth in Chicks

Chu

Kee

2015

PLoS ONE

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PurposeTo determine the effects of optically imposed astigmatism on early eye growth in chicks.Methods5-day-old (P5) White Leghorn chicks were randomly assigned to either wear, monocularly, a “high magnitude” (H: +4.00DS/-8.00DC) crossed-cylindrical lens oriented at one of four axes (45, 90, 135, and 180; n = 20 in each group), or were left untreated (controls; n = 8). Two additional groups wore a “low magnitude” (L: +2.00DS/−4.00DC) cylindrical lens orientated at either axis 90 or 180 (n = 20 and n = 18, respectively). Refractions were measured at P5 and after 7 days of treatment for all chicks (P12), whereas videokeratography and ex-vivo eyeshape analysis were performed at P12 for a subset of chicks in each group (n = 8).ResultsCompared to controls, chicks in the treatment groups developed significant amounts of refractive astigmatism (controls: 0.03±0.22DC; treatment groups: 1.34±0.22DC to 5.51±0.26DC, one-way ANOVAs, p≤0.05) with axes compensatory to those imposed by the cylindrical lenses. H cylindrical lenses induced more refractive astigmatism than L lenses (H90 vs. L90: 5.51±0.26D vs. 4.10±0.16D; H180 vs. L180: 2.84±0.44D vs. 1.34±0.22D, unpaired two-sample t-tests, both p≤0.01); and imposing with-the-rule (H90 and L90) and against-the-rule astigmatisms (H180 and L180) resulted in, respectively, steeper and flatter corneal shape. Both corneal and internal astigmatisms were moderately to strongly correlated with refractive astigmatisms (Pearson’s r: +0.61 to +0.94, all p≤0.001). In addition, the characteristics of astigmatism were significantly correlated with multiple eyeshape parameters at the posterior segments (Pearson’s r: -0.27 to +0.45, all p≤0.05).ConclusionsChicks showed compensatory ocular changes in response to the astigmatic magnitudes imposed in this study. The correlations of changes in refractive, corneal, and posterior eyeshape indicate the involvement of anterior and posterior ocular segments during the development of astigmatism.

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Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Effects of Optically Imposed Astigmatism on Early Eye Growth in Chicks

Chu

Kee

2015

PLoS ONE

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“…At the end of the one-week treatment period, a modified Hartinger refractometer 54 was used to identify birds that had developed high magnitudes of myopia (<−10D) and refractive astigmatism (>2D). Of the 39 treated birds, eight fulfilled these refractive-error criteria and additional biometric measures were taken to determine the corneal parameters and ocular axial dimensions by means of a custom-made corneal topographer 55 and a high resolution (20 mHz) A-scan ultrasonography system, respectively 52 . Refractometry and A-scan ultrasonography were carried out while birds were anaesthetized (isoflurane inhalation, 1.0% to 1.5% in oxygen) whereas corneal topography were measured in awake chicks 55 .…”

Section: Methodsmentioning

confidence: 99%

Region-specific differential corneal and scleral mRNA expressions of MMP2, TIMP2, and TGFB2 in highly myopic-astigmatic chicks

Yip

Shan

et al. 2017

Sci Rep

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Myopia and astigmatism, two common refractive errors frequently co-exist, are affecting vision at all working distances in the affected populations worldwide. Eyeballs having these refractive errors are known to exhibit abnormal eye shape at the anterior and posterior eye segments, but whether the outer coats of these abnormal eyeballs, cornea anteriorly and sclera posteriorly, are regulated by region-specific molecular mechanism remains unclear. Here we presented the changes in mRNA expression levels of three genes (MMP2, TIMP2, and TGFB2), all known to participate in extracellular matrix organization, at five regions of the cornea and sclera in chickens developing high myopia and astigmatism induced by form deprivation. We found that, compared to normal chicks, the highly myopic-astigmatic chicks had significantly higher expression of all three genes in the superior sclera (Mann-Whitney tests, all p ≤ 0.05), as well as higher TIMP2 expression in the central cornea and nasal sclera (Mann-Whitney tests, both p ≤ 0.05). Strikingly, the superior scleral region stood out as showing the strongest and most widespread correlations between mRNA expression and biometry parameters including axial and astigmatic components (r = + 0.52~ + 0.85, all p < 0.05). These results imply that local molecular mechanism may manipulate the eye shape remodeling across the globe during refractive-error development.

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