Scleral biomechanics in the aging monkey eye

Area of Science:

• Ophthalmology
• Biomechanical Engineering
• Gerontology

Background:

• The sclera's biomechanical properties are crucial for maintaining ocular integrity and function.
• Understanding age-related changes in scleral biomechanics is essential for addressing vision loss conditions.

Purpose of the Study:

• To investigate age-related differences in the biomechanical properties of posterior sclera in rhesus monkeys.
• To compare young and old rhesus monkey sclera regarding inhomogeneity, anisotropy, and nonlinearity.

Main Methods:

• Posterior scleral shells were subjected to elevated intraocular pressure (IOP) in a pressurization apparatus.
• 3D displacements were measured using speckle interferometry, and geometry was reconstructed via 3D digitizer and ultrasound.
• An inverse finite element method with a fiber-reinforced model was used to determine biomechanical properties.

Main Results:

• The posterior sclera demonstrated inhomogeneous, anisotropic, and nonlinear mechanical behavior.
• Older monkeys exhibited significantly thinner sclera with higher tangent modulus and structural stiffness compared to younger monkeys.
• Collagen fiber orientation around the optic nerve head (ONH) was predominantly circumferential, with no age-related differences in orientation or concentration.

Conclusions:

• Older monkey posterior sclera is significantly stiffer than younger monkey sclera.
• Increased scleral stiffness in older monkeys leads to higher stress and lower strain under elevated IOP.
• Age-related scleral stiffening may impact optic nerve head biomechanics and contribute to glaucoma susceptibility.