Permeability of the porcine iris stroma

Abstract

Current literature has not considered or provided any data on the permeability of the iris stroma. In this study, we aimed to determine the hydraulic permeability of porcine irides from the isolated stroma. Fifteen enucleated porcine eyes were acquired from the local abattoir. The iris pigment epithelium was scraped off using a pair of forceps and the dilator muscles were pinched off using a pair of colibri toothed forceps. We designed an experimental setup, based on Darcy's law, and consisting of a custom 3D-printed pressure column using acrylonitrile butadiene styrene (ABS) plastic. PBS solution was passed through the iris stroma in a 180° arc shape, with a column height of approximately 204 mm (2000 Pa). Measurements of iris stromal thickness were conducted using optical coherence tomography (OCT). To measure flow rate, we measured the mass (volume) of PBS solution using a mass balance in approximately 1 min. Histology was performed using hematoxylin and eosin (H&E) and anti-smooth muscle antibody (anti-α-SMA) for validation. The permeability experiments demonstrated that the iris stroma is a biphasic tissue that allows fluid flow. Our image processing results determined the area of flow to be 7.55 mm² and the tissue thickness to be between 180 and 430 μm. The hydraulic permeability of the porcine stroma, calculated using Darcy's law, was 5.13 ± 2.39 × 10^-5 mm²/Pa•s. Histological and immunochemical studies confirmed that the tissues used for this permeability study were solely iris stroma. Additionally, anti-α-SMA staining revealed staining specific for stromal blood vessels, with the notable absence of dilator and sphincter muscle staining. Our study combined experimental microscopic data with the theory of biphasic materials to investigate the hydraulic permeability of the iris stroma. This work will serve as a basis on which to validate future biomechanical studies of human irides with which may ultimately aid disease diagnosis and inform the design of novel treatments.

Keywords: Angle closure glaucoma; Aqueous humor; Biphasic tissue; Dilator muscles; Hydraulic permeability; Iris biomechanics; Iris pigment epithelium; Sphincter muscles.