Linear Viscoelasticity of Human Ocular Tissues During Tensile Stress Relaxation

To quantitatively describe viscoelastic properties, we characterized the tensile stress relaxation of human ocular tissues using a Prony series model.

Specimens from eight pairs of postmortem human eyes were dissected from six regions: the anterior, equatorial, posterior, and peripapillary sclera; the optic nerve (ON); and the optic nerve sheath (ONS). Each specimen underwent uniaxial tensile loading under controlled physiological conditions at strain levels ranging from 4% to 6% to identify the optimal strain range within which the tissues exhibit linear viscoelastic behavior. Stress relaxation curves were fitted to a generalized Maxwell model using a Prony series to determine tissue-specific relaxation time constants and relative moduli.

All tissues exhibited linear viscoelastic behavior within 5% strain. The anterior sclera showed the greatest stress level, with 12.6 MPa instantaneous modulus and 8.8 MPa equilibrium modulus, whereas the ON exhibited the fastest stress decay and lowest stiffness, with moduli of 3.5 MPa and 1.1 MPa, respectively. The ON had the longest long-term relaxation time of 460 ± 77 seconds, and the ONS had the shortest time at 60 ± 5 seconds. Prony series parameters successfully captured the relaxation profiles across all tissues.

This study supports the use of Prony-based models for numerical simulation to describe the region-specific viscoelasticity of ocular tissues. These findings provide foundational data for future investigations into ocular biomechanics, particularly under dynamic or pathologic loading.