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K. M. Myers, F. Cone, H. Quigley, T. Nguyen; Age Effects on the Inflation Response of C57/BL6 Mouse Sclera. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2130.
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To measure the time-dependent inflation response of intact C57/BL6 mouse sclera to increases in intraocular pressure, comparing old (11 month) and young (2 month) animals.
Eyes from C57/BL6 (2 and 11months) mice were enucleated, mounted by gluing the cornea to a custom fixture, cannulated and immersed in PBS. An active feedback, pressure-controlled syringe pump inflated the cannulated eyes in a series of load-unload and ramp-hold creep tests. First, the eyes were loaded from 6mmHg to15mmHg (0.5mmHg/s) and then immediately unloaded to 6mmHg for 5 minutes. This load-unload was repeated two additional times. Specimens were then loaded to 10.5mmHg for 30 minutes and unloaded to 6mmHg for 10 minutes. This creep test was repeated to pressure levels of 15, 22.5, 30, 37.5, and 45mmHg. A CCD video camera attached to a microscope imaged the expanding scleral surface at 0.5Hz (5µm/pixel). Scleral displacement was measured with a digital image correlation (DIC) program (Correlated Solutions Inc., Vic 2-D). After testing, fresh tissue thickness measurements were taken on scleral slices at multiple locations under a light microscope.
Sclera from older C57/BL6 mice was stiffer than younger C57/BL6 sclera (Student’s t-test, p<0.05). The secant moduli measured in the small-strain (6-15mmHg) and the large-strain (15-45mmHg) regime, respectively, were 1,670±370 kPa and 8,590±2,890kPa for the old and 890±390kPa and 5,050±1,070kPa for the young. Both old and young specimens showed evidence of creep during the ramp-hold tests, with a statistically significant increase in the creep rate with increasing pressure for the younger tissue (Student’s t-test, p<0.05).
Age has a stiffening effect on the mechanical properties of C57/BL6 mouse sclera. In addition, the creep rate for the younger scleral tissue is pressure-dependent. Future stress analysis will include specimen-specific finite element analysis, and examination of the effects of induced and spontaneous glaucoma in mouse models.
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