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Fan Yuan, Lucinda Camras; Local Stiffness of Rat Trabecular Meshwork. Invest. Ophthalmol. Vis. Sci. 2013;54(15):75.
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Stiffness of trabecular meshwork (TM) may play an important role in regulating outflow resistance in healthy and glaucomatous eyes (Last et al., 2011; Camras, et al., 2012). To investigate its effects on pathogenesis of glaucoma in rodent models, we developed a technique to determine TM stiffness in rat eyes using atomic force microscopy (AFM).
Rat eyes were enucleated immediately after death and perfused with Evans Blue dye (0.5 mg/mL) for 15 min. The dye perfusion allowed us to better visualize TM location in subsequent tissue dissection and tissue assignment with the AFM probe. Incisions were made in the posterior sclera to remove the iris, lens, choroid, and retina leaving only the ocular shell (cornea, sclera, and TM) intact. The shell, with the TM facing upwards, was flat mounted to a petri dish using glass coverslips. Histological examination was performed to check any damages of TM caused by tissue dissection. A probe with gold-coated colloid (5 µm in diameter) was used to indent the cornea, sclera, and TM at a velocity of 5 µm/sec. The Hertz equation was used to calculate the Young’s modulus (E) of tissues.
The average Young’s modulus of TM was 91.4 ± 0.6 Pa, which was lower than the stiffness of cornea and sclera measured in the same eye. Histological examination confirmed that TM structures were still intact post-dissection. Additional studies are being conducted to determine the accuracy of measurements and regional variation of E in the ocular shell.
A rat model was developed for investigation of TM stiffness and its effects on outflow resistance. The enabling technique developed in this study will allow investigators to use the rat model to evaluate mechanisms of TM stiffness changes related to aging or pathogenesis of glaucoma. It can also be used to study efficacies of interventions and drug treatments that are designed to modulate TM stiffness.
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