Abstract
Purpose :
To characterize the porovisco-hyperelastic properties of porcine lenses through compression tests using optical coherence elastography (OCE) and inverse finite element analysis (iFEA).
Methods :
13 porcine lenses obtained from a local slaughterhouse were used. The test initially consisted in axially compressing the lens’ thickness (LT) to 6.00 mm whilst the force required to achieve this deformation state was registered. Then, a sinusoidal micro-displacement (~34 um) with a period of 5 s controlled by a piezoelectric actuator was applied to the compressed lens whilst 2D strain maps of the lens (Fig. A) were computed using OCE. The overall test recording was 7.6 s, consisting of 256 subsequent B-scans, and the piezoelectric actuator began to displace at 0.8 s from the start of the acquisition (Fig. B). The strain maps and the force applied were used to determine the mechanical properties of the lens using iFEA. Different modeling approaches, including poroviscoelastic, viscoelastic, and stiffness gradient models, were considered.
Results :
The accuracy of the OCE strains was confirmed by comparing them to the known LT strains, used as reference in this displacement-controlled test (Fig. C). We found that the averaged anterior strains were larger than those of the nucleus (7.32 10-3 compared to 6.11 10-3 ,respectively). The posterior cortex presented the lowest strains at 5.37 10-3. The results also demonstrated a pronounced viscoelastic behavior of the lens nucleus, as evidenced by the time delay between the LT strains and those of the nucleus at the midpoint of the sinusoidal displacement (t=2.50 s). The nucleus 'delay' ranged from 2.50 10-2 to 8.51 10-2 s and the LT ranged from 7.55 to 8.10 mm. The experimentally observed strain oscillation amplitudes could be reconstructed in the iFEA with a MAPE lower than 5% considering the lens stiffness gradient model.
Conclusions :
The findings suggest that the anterior cortex is softer than the lens nucleus for most of the lenses (9/13) under investigation. The posterior cortex appears to be the stiffest part. The lens nucleus exhibits a rapid viscoelastic effect (τ~1s using Prony Series).
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.