The influence of lamellar orientation on corneal material behavior: biomechanical and structural changes in an avian corneal disorder.
OBJECTIVE
Retinopathy, globe enlarged (RGE) is an inherited genetic disease of chickens with a corneal phenotype characterized by loss of tissue curvature and changes in peripheral collagen fibril alignment. This study aimed to characterize the material behavior of normal and RGE chicken corneas under inflation and compare this with new spatial- and depth-resolved microstructural information to investigate how stromal fibril architecture determines corneal behavior under intraocular pressure (IOP).


METHODS
Six RGE chicken corneas and six age-matched normal controls were tested using trephinate inflation and their stress-strain behavior determined as a function of posterior pressure. Second harmonic generation mulitphoton microscopy was used to compare the in-plane appearance and degree of through-plane interlacing of collagen lamellae between normal and mutant corneas.


RESULTS
RGE corneas displayed a 30-130% increase in material stiffness [E(tangent)(RGE) = 0.94 ± 0.18 MPa to 3.09 ± 0.66 MPa; E(tangent)(normals) = 0.72 ± 0.13 MPa to 1.34 ± 0.35 MPa] (P ≤ 0.05). The normal in-plane disposition of anterior collagen in the peripheral cornea was altered in RGE but through-plane lamellar interlacing was unaffected.


CONCLUSIONS
This article demonstrates changes in corneal material behavior in RGE that are qualitatively consistent with microstructural collagen alterations identified both herein and previously. This study indicates that, in general, changes in stromal fibril orientation may significantly affect corneal material behavior and thereby its response to IOP.
Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom. bootec@cf.ac.uk
Craig
C
Boote
Ahmed
A
Elsheikh
Wael
W
Kassem
Christina S
CS
Kamma-Lorger
Paul M
PM
Hocking
Nick
N
White
Chris F
CF
Inglehearn
Manir
M
Ali
Keith M
KM
Meek
D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology*; D001766:Blindness / Q000235:genetics / Q000473:pathology / Q000662:veterinary*; D002645:Chickens; D003094:Collagen / Q000378:metabolism*; D003316:Corneal Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D003319:Corneal Stroma / Q000378:metabolism* / Q000503:physiopathology; D004547:Elastic Tissue; D006984:Hypertrophy; D007429:Intraocular Pressure; D036641:Microscopy, Fluorescence, Multiphoton; D011201:Poultry Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D012162:Retinal Degeneration / Q000235:genetics / Q000473:pathology / Q000662:veterinary*
D003094:Collagen