Fluctuations in intraocular pressure increase the trabecular meshwork extracellular matrix.

BACKGROUND/AIMS The trabecular meshwork (TM) tissue is constantly exposed to dynamic stress caused by intraocular pressure (IOP). The effects of such biomechanical stress on the TM have not been analyzed. This study developed an animal model of fluctuating IOP and evaluated the effects of these fluctuations on TM tissue. METHODS To create fluctuation in the IOP, one eye of adult SD rats was exposed to cyclic stress with IOP fluctuation ranging from 5 mmHg to 45 mmHg at a 1/60 Hz frequency for 30 minutes every day for several weeks. The other eye was not treated and served as the control. Hematoxylin-eosin staining was used to evaluate changes in the ganglion cells and the morphology, thickness and density of the TM; immunohistochemistry was used to detect α-smooth muscle actin (α-SMA), laminin (LA) and fibronectin (FN) expression in the TM. RESULTS After several weeks of daily IOP fluctuation, the TM thickness remained unchanged, whereas the density dramatically increased. α-SMA, LA and FN were expressed in rat TM tissue, and the percentages of areas with positive expression significantly increased. The IOP was similar in the treated and control eyes and only tended to increase on day 22 of the experiment. Throughout the 28-day experiment, no ganglion cells were lost. CONCLUSIONS Large fluctuations in IOP promoted the synthesis of α-SMA, LA and FN in the TM and increased the density of the TM, suggesting that fluctuations in IOP can induce pathological changes in the TM.