Abstract
Purpose :
Presbyopia affects everyone as we age and is deeply linked to mechanical properties of the lens. The lack of in vivo characterization of lens mechanical properties is a major barrier towards the development of new therapies that address the biomechanical nature of the disease. In this study the crystalline lens spatial-varying mechanical properties are characterized in relation to their overall elastic modulus, and their structural-functional role in accommodation loss is demonstrated.
Methods :
We analyzed fresh porcine lenses with biopsy punches and gold standard mechanical compression testing to evaluate the lens spatial dimension effects on overall elastic modulus. We measured porcine lenses with Brillouin microscopy to characterize the spatial-varying mechanics. Next, we used in vivo Brillouin microscopy data to validate the effects of changing spatial-varying modulus and geometry on accommodation amplitudes using a structural-optical model of accommodation.
Results :
Compression data show that porcine lenses have a higher nucleus modulus than cortex modulus, ranging from 2.14 kPa to 15.0 kPa as the biopsy diameter decreased. Incorporating a spatial-varying 2-component model, the cortex modulus and nucleus modulus were extracted as 1.14 kPa and 15 kPa respectively. The spatially-averaged Brillouin modulus was found to agree empirically with the overall elastic modulus of the lens in a log-log relationship. The structural-optical model using patient Brillouin data saw an accommodation amplitude drop from 5.91 D in the 19YO to 1.74 D in the 61YO when considering both modulus and geometry changes, 2.85 D when considering stiffness changes alone, and 4.85 D when considering geometry changes alone.
Conclusions :
Overall, our results demonstrate the 2-component model of the nucleus and cortex, and how spatial changes in nucleus percentage dominate mechanical properties of the lens. An empirical log-log relationship was established between Brillouin microscopy and overall elastic modulus. The structural-optical modeling agrees with loss of accommodation trends and suggests that stiffness changes in the lens dominate this loss of accommodation rather than lens geometry changes.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.