The Structural Layers of the Porcine Iris Exhibit Inherently Different Biomechanical Properties.
Tan Royston K Y, Panda Satish K, Braeu Fabian A, Muralidharan Arumugam R, Nongpiur Monisha E, Chan Anita S Y, Aung Tin, Najjar Raymond P, Girard Michaël J A
AI Summary
This study found porcine iris stroma is permeable and biomechanically distinct from the dilator muscle, offering insights into angle-closure glaucoma mechanisms.
Abstract
Purpose
The purpose of this study was to isolate the structural components of the ex vivo porcine iris tissue and to determine their biomechanical properties.
Methods
The porcine stroma and dilator tissues were separated, and their dimensions were assessed using optical coherence tomography (OCT). The stroma underwent flow test (n = 32) to evaluate for permeability using Darcy's Law (ΔP = 2000 Pa, A = 0.0391 mm2), and both tissues underwent stress relaxation experiments (ε = 0.5 with initial ramp of δε = 0.1) to evaluate for their viscoelastic behaviours (n = 28). Viscoelasticity was characterized by the parameters β (half width of the Gaussian distribution), τm (mean relaxation time constant), E0 (instantaneous modulus), and E∞ (equilibrium modulus).
Results
For the stroma, the hydraulic permeability was 9.49 ± 3.05 × 10-6 mm2/Pa · s, and the viscoelastic parameters were β = 2.50 ± 1.40, and τm = 7.43 ± 4.96 s, with the 2 moduli calculated to be E0 = 14.14 ± 6.44 kPa and E∞ = 6.08 ± 2.74 kPa. For the dilator tissue, the viscoelastic parameters were β = 2.06 ± 1.33 and τm = 1.28 ± 1.27 seconds, with the 2 moduli calculated to be E0 = 9.16 ± 3.03 kPa and E∞ = 5.54 ± 1.98 kPa.
Conclusions
We have established a new protocol to evaluate the biomechanical properties of the structural layers of the iris. Overall, the stroma was permeable and exhibited smaller moduli than those of the dilator muscle. An improved characterization of iris biomechanics may form the basis to further our understanding of angle closure glaucoma.
MeSH Terms
Shields Classification
Key Concepts5
The hydraulic permeability of the porcine iris stroma was 9.49 ± 3.05 × 10-6 mm2/Pa · s, as determined using a flow test (ΔP = 2000 Pa, A = 0.0391 mm2) on 32 samples.
The viscoelastic parameters for the porcine iris stroma were β = 2.50 ± 1.40, τm = 7.43 ± 4.96 s, E0 = 14.14 ± 6.44 kPa, and E∞ = 6.08 ± 2.74 kPa, derived from stress relaxation experiments (ε = 0.5 with initial ramp of δε = 0.1) on 28 samples.
The viscoelastic parameters for the porcine iris dilator tissue were β = 2.06 ± 1.33, τm = 1.28 ± 1.27 seconds, E0 = 9.16 ± 3.03 kPa, and E∞ = 5.54 ± 1.98 kPa, derived from stress relaxation experiments (ε = 0.5 with initial ramp of δε = 0.1) on 28 samples.
The porcine iris stroma exhibited smaller moduli (E0 = 14.14 ± 6.44 kPa and E∞ = 6.08 ± 2.74 kPa) compared to the porcine iris dilator muscle (E0 = 9.16 ± 3.03 kPa and E∞ = 5.54 ± 1.98 kPa).
A new protocol was established to evaluate the biomechanical properties of the structural layers of the iris, involving separation of stroma and dilator tissues, dimension assessment by optical coherence tomography (OCT), flow tests for permeability, and stress relaxation experiments for viscoelastic behaviors.
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