Simultaneous measurement of strains of the aqueous veins and perilimbal sclera in porcine and human globes using photoacoustic microscopy and finite elements analysis

Abstract

Purpose : Despite knowledge of clinical risk factors and effective treatments to lower intraocular pressure (IOP), clinicians remain challenged to predict IOP outcomes for glaucoma treatment. For newer glaucoma surgeries that target Schlemm’s canal (SC), there is great interest to gain knowledge on outflow resistance distal to the trabecular meshwork and SC. The purpose of this study is to understand the biomechanical interactions between the aqueous veins and the surrounding perilimbal sclera and their correlation with IOP regulation.

Methods : We developed a photoacoustic microscopy (PAM) system for simultaneous and separate resolution of the anatomies of aqueous veins and perilimbal sclera in 3D (Fig. 1a). Aqueous veins are identified by 0.25% ICG tracer perfusion in whole globes (Fig. 1b-e). The strains within the tissue components are quantified by finite element analysis (FEA, Fig. 1f-g) during IOP elevation in porcine and human globes.

Results : The maximum and minimum principal strains of points on the imaged aqueous vein (Fig 1) are respectively in-plane (red arrows) and out-of-plane (blue arrows). This behavior is reflected by the deformation of the vein cross-section in Fig. 1j. Collagen fibers in the scleral tissue are predominantly organized in-plane within the scleral thickness. Therefore, though the overall mechanics is complex, an important interaction is that resistance of aqueous vein deformation by the surrounding sclera is mostly in-plane, and large collagen stiffness can act to restrict in-plane expansion of the vein. In this study, we focus on comparing the maximum principal strains of the veins and sclera, which are both in-plane. Fig. 2a-b show a strong correlation between these strains during IOP variations (R²=0.73, n=8). Fig. 2b shows that the tensile strain in the aqueous veins is restricted by the strain in the sclera, which is reduced when the sclera is stiff. Fig. 2c-d show a strong correlation between the biomechanical properties of limbus/perilimbal sclera and IOP (R²=0.78, n=6).

Conclusions : The imaging data and strains indicate that the perilimbal sclera influences the deformation of aqueous veins. Future studies will comprehensively analyze the strains quantified by PAM-FEA in 3D to determine correlations between the biomechanical behaviors of the tissue components and IOP regulation.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.