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Matthew James Alan Rickard, Creed Jones, Jonathan Cox, James DeVore, Alma Castro, Jonathan Brannen; Scleral strain near the limbus using digital microscopy of natural features in porcine eyes.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6138.
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To measure the meridional scleral strain near the limbus at pressure levels indicative of a patient experiencing high intraocular pressure.
Porcine eyes were used within 36 hours postmortem. Twelve scalded and twelve non-scalded eyes were purchased through a local supplier (Sierra-Medical.com) for comparison. Of the scalded eyes, six of them were purchased with heads and remained in the three heads during the experiment. All other eyes were purchased enucleated. Each eye was pressurized using a distilled water column raised initially to 39 mmHg and then lowered to 12 mmHg. In all cases, steady flow was reached to ensure eye volume stabilized. A pressure sensor (Honeywell) and an ultra-low liquid flow sensor (Sensirion) monitored the pressure and flow, respectively. The liquid column was attached to tubing that terminated with a 27-gauge needle. The needle pierced through the cornea at the limbus approximately 6 clock hours opposite the tissue under observation. A digital microscope (Keyence) imaged natural features (blood vessels) in a 3-mm-wide zone near the limbus. Images were captured for both 39 and 12 mmHg and were manually aligned using a feature near the limbus. A second feature, typically about 2 mm away in the meridional direction, was then identified. For each image, the feature pair was selected based on largest observed strain. The distance between the two features for the two pressure levels were compared based on image pixel values in order to determine the meridional strain.
For the scalded eyes, the values for the two enucleated eyes with the largest observed strains were 3.06% and 3.16%; a maximum value of 1.33% was seen for the intact eyes. For the non-scalded eyes, the eyes with the largest observed strains showed values of 3.06%, 3.40%, and 3.07%. All values have a measurement tolerance of +/- 0.15 %. The maximum observed meridional strain at the limbus was found vary from eye to eye and in some cases was negligible, though circumferential strain was noted in those cases. This variation can explained by the fact that only one small, selected portion of the limbus (6 clock hours from the random incision site) could be viewed. The data indicate that maximum strain, when viewable, is near 3%.
Maximum meridional strain near the limbus was found to be approximately 3% in porcine eyes (scalded or non-scalded) at an intraocular pressure of 39 mmHg.
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