Changes in the biomechanical response of the optic nerve head in early experimental glaucoma.
OBJECTIVE
To investigate the biomechanical response of the optic nerve head (ONH) connective tissues to IOP elevation in three pairs of monkey eyes in which one eye had early experimental glaucoma (EG).


METHODS
A serial imaging technique was used to reconstruct the ONH and peripapillary sclera of three pairs of unilateral EG eyes fixed at 10 mm Hg. Eye-specific finite element models of the posterior pole were constructed with inhomogeneous material properties defined for the lamina cribrosa (LC) based on local connective tissue volume fraction (CTVF) and predominant LC beam orientation. These models were used to simulate an IOP increase from 10 to 45 mm Hg. A laminar material constant was varied to produce a range of LC displacements and scleral canal expansions, and the associated LC stress and strain were characterized.


RESULTS
The models suggest that the LC of normal and EG eyes can deform posteriorly or anteriorly when the LC material stiffness is low or high, respectively. Scleral canal expansion was generally, but not always, reduced in EG eyes. Strains in the EG eye were similar to or lower than those in the contralateral eye for the same average LC displacement and increased when the LC was more plaint. Laminar stresses were consistently lower in the EG eye, regardless of LC stiffness.


CONCLUSIONS
Connective tissue remodeling in EG alters the biomechanical response of the LC to IOP elevation in an eye-specific manner. The models indicated that the LC tissues in EG eyes were more plaint than those in the contralateral normal eyes in two of three monkeys.
Ocular Biomechanics Laboratories, Devers Eye Institute, Legacy Health System, Portland, Oregon 97232, USA.
Michael D
MD
Roberts
Ian A
IA
Sigal
Yi
Y
Liang
Claude F
CF
Burgoyne
J Crawford
JC
Downs
D000818:Animals; D001696:Biomechanical Phenomena; D003238:Connective Tissue / Q000502:physiology*; D004195:Disease Models, Animal; D020342:Finite Element Analysis; D005901:Glaucoma / Q000503:physiopathology*; D007429:Intraocular Pressure; D008252:Macaca fascicularis; D008297:Male; D009898:Optic Disk / Q000502:physiology*; D009901:Optic Nerve Diseases / Q000503:physiopathology*