The effect of high myopia on corneal changes in chicken

Abstract

Purpose: To investigate changes in corneal biometric and biomechanical parameters by applying custom-made instruments and proteomic analysis during the development of high myopia in form-deprivation treated chicks. Methods: White Leghorn chicks (Gallus gallus domesticus) were used. Form-deprivation myopia was induced by occluding the right eyes for a week from day 5 post-hatching, while left eyes served as fellow contralateral controls. Refractive status, ocular axial dimensions, and corneal curvature were measured by a modified Hartinger refractometer, high-frequency A-scan ultrasonography, and custom-made videokeratography, respectively. Experiment 1 (Chapter 2): The applicability of a custom-made air-jet optical coherence tomography system for corneal biomechanics measurement on chicks was tested. An intraocular-pressure control system was also validated. Experiment 2 (Chapter 3): The applicability of a custom-made optical-coherence­tomography-indentation probe system for corneal biomechanics measurement on chicks was tested. The relationship between corneal biomechanical properties (tangent modulus and stiffness coefficient) and ocular biometric parameters was investigated. Experiment 3 (Chapter 4): Generation and application of the chicken corneal proteome for a screening of differentially expressed corneal proteins during the change of corneal biometric and biomechanical properties in high myopia. Results: Experiment 1 (Chapter 2): The custom-made air-jet optical coherence system was applicable for the measurement of chicks' eyes and a reduced corneal stiffness coefficient was found in form-deprivation treated eyes (mixed two-way ANOVA; main effect of myopia treatment: F (1, 24)= 17.13, p<0.001). Experiment 2 (Chapter 3): The custom-made optical-coherence-tomography­indentation probe system was shown to be reliable and valid for corneal biomechanics measurements. Highly myopic chicks had a reduced corneal tangent modulus and stiffness coefficient (mixed two-way ANOVAs, all p<0.01). A significant correlation was observed between corneal biomechanical properties and ocular biometric parameters (with spherical equivalent refractive error, all r>+0.52, p<0.05; with vitreous chamber depth, all r>-0.61, p<0.05). Experiment 3 (Chapter 4): A large corneal proteome of the chick (n= 2096) was established (1 % Global FDR). Using this first reported spectral library for highly myopic chicks, three upregulated (Reactive intermediate imine deaminase A homolog, Cadherin-1, and RuvB-like helicase) and five downregulated (Fibrinogen alpha chain, Fibrinogen beta chain, Fibrinogen gamma chain, Alpha-2­macroglobulin-like 4, and Chromobox 3 protein) proteins were identified following application of mass-spectrometry based proteomic analysis (p<0.05). Conclusions: These results demonstrated significant changes in the corneal biometric and biomechanical properties as a result of the development of high myopia in chicks. The establishment of a corneal proteome in chicken provides research opportunities to study mechanisms potentially involved in corneal reshaping.