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Barbara Murienne, Joan Jefferys, Harry Quigley, Thao D Nguyen; Contribution of glycosaminoglycans to the mechanical behavior of the posterior sclera. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4259.
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To investigate contribution of glycosaminoglycans (GAGs) to the mechanical behavior of the posterior sclera
We measured the inflation response of porcine posterior scleras, comparing 3 experimental groups: control, buffer-treated, and enzyme-treated (Murienne, et al. IOVS 2013;54:ARVO E-Abstract 52). Here, we report differences in GAG content, hydration (wet/dry weight), thickness and mechanical behavior between the 3 groups and 4 quadrants of the eye (SN, ST, IN, IT). Enzyme- and buffer-treated samples were incubated in chondroitinaseABC in buffer or buffer alone. Mechanical outcomes were the slope of the pressure-strain loading curve at low and high pressures, hysteresis (area under the load-unload curve), strain at maximum pressure, and creep rate (slope of the strain-time curve after 80s) in the circumferential and meridional directions. Generalized estimating equation and mixed linear models with Bonferroni adjustment were used for statistical analysis.
There was an 81.5% mean decrease in GAG content in enzyme-treated sclera compared to buffer-treated (p< 0.0001), but no significant difference between control and buffer-treated groups. In control and buffer-treated groups, the GAG content was higher in superior than inferior quadrants (p≤0.004). Compared to control, mean hydration increased by 7% with buffer treatment (p=0.001) and by 6% with enzyme treatment (p=0.002) compared to buffer-treatment. With buffer treatment, mean thickness increased by 8% over control (p<0.0001), but buffer and enzyme treated groups were not significantly different. Compared to control, the circumferential strain response of buffer-treated specimens showed an increase in the mean low pressure slope (30%, p<0.0001), creep rate (70%, p<0.0001), and hysteresis (0.05, p=0.04). In comparison to buffer-treated, enzyme-treated specimens showed a decrease in the mean low pressure slope (-50%, p<0.0001) and hysteresis (-0.07, p=0.004); but an increase in the creep rate (30%, p<0.0001) and strain at maximum pressure (0.01, p<0.0001). Analysis for difference between the control vs. buffer and buffer vs. enzyme comparisons were statistically significant for all mechanical outcomes (p<0.01) except for the creep rate. Similar results were found the meridional strains.
Enzyme treatment was effective in removing GAGs. GAG removal affected the load-unload pressure-strain and creep strain-time response.
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