Circumferential tensile stiffness of glaucomatous trabecular meshwork

Our previous work indicated that a larger circumferential Young's modulus (E) of trabecular meshwork (TM) correlated with a higher outflow facility (C) in normal human donor eyes. The current study investigated the influence of glaucomatous TM stiffness and cellularity on C.

Eight left eyes from glaucomatous human donors were perfused within 48 hours post mortem. Values of C were determined at pressures of 10, 20, 30, and 40 mm Hg. The TM was then dissected and imaged with optical coherence tomography to determine its cross-sectional area. Uniaxial tensile stress was applied longitudinally to TM segments to determine stress-strain curves. E was calculated at zero strain, representing the circumferential stiffness of the TM at a relaxed state. Confocal images of DAPI-stained TM segments were used to determine cellularity after mechanical stretching.

C (μL/min/mm Hg) of glaucomatous eyes was 0.18 ± 0.02 (mean ± SE) at 10 mm Hg and decreased to 0.11 ± 0.02 when the pressure was increased to 40 mm Hg. C measured at 30 and 40 mm Hg correlated with TM cellularity. E was 12.5 MPa and 1.4 (geometric mean and SE) and did not statistically correlate with postmortem time, age, C, or cellularity.

Compared with data of normal eyes observed in a previous study, C in glaucomatous eyes was reduced significantly, and the amount of reduction increased with increasing the pressure. E of glaucomatous TM was approximately one-fifth that of normal TM. Prospective studies are needed to further investigate the influence of TM tensile stiffness on outflow regulation.