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B. Coudrillier, K. M. Myers, H. A. Quigley, C. Boote, T. D. Nguyen; The Biomechanical Response of Normal and Glaucoma Human Sclera. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5562.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the mechanical response to controlled inflation and the regional thickness variations of the sclera between normal and glaucoma human post-mortem eyes.
Three glaucoma eyes (from 2 persons) and 4 normal human eyes (from 2 persons) were tested within 48 hours post-mortem. The sclera was incised 3 mm posterior to the equator, glued to a plastic ring, and mounted on an inflation chamber. Prior to testing, scleral thickness was measured with an ultrasonic pachymeter at 16 sites. The specimen was inflated by pressure controlled injection of balanced salt solution through a series of load-unload tests from 1 mmHg to 30 mmHg at 3 pressure rates (0.05, 1, 5 mmHg/s), separated by a recovery period. Two cameras imaged the deforming scleral surface at 0.5 Hz to permit three dimensional displacement mapping using a Digital Image Correlation program.
Glaucoma specimens were stiffer than normal sclera. Displacements were greatest in the peripapillary sclera in all eyes. The maximum radial displacement was on average 2.5 times larger for normal eyes. The tangent modulus at 15 mmHg was 0.29 ± 0.1 MPa for normal eyes and 0.38 ± 0.11 MPa for glaucoma eyes. This difference may be associated with an alteration in collagen fiber density, as indicated by x-ray scattering results from a glaucoma specimen. For normal and glaucoma eyes, the superior-temporal quadrant of the peripapillary sclera was the thickest and the nasal-inferior quadrant was the thinnest (1.05 mm for the superior, 1.01 mm for the temporal, 0.72 mm for the nasal, 0.80 mm for the inferior; standard deviation < 0.19 mm for each pole).
Pilot in vitro biomechanical data on a small number of eyes suggest that glaucoma eyes have stiffer sclera, as reported by indirect methods in vivo. We are now examining the potential modifying effects of age, gender, and ethnicity along with glaucoma on scleral biomechanical behavior.
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