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Mark P. Breazzano, Michael Fikhman, Jerrold L. Abraham, Ann E. Barker-Griffith; Schwalbe’s Line (Limbal Smooth Zone) is Wider Superiorly than Naso-inferiorly: A Scanning Electron Microscopic Study of Eye Bank Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4907.
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Assess the relationship between radial location and Schwalbe’s line by examining the width of the smooth zone at various ages.
Full corneal-scleral rings were extracted from twenty-six formalin-fixed human donor eyes dehydrated in ethanol, and dried from acetone. Imaging of the smooth zone with scanning electron microscopy (SEM) yielded a montage for each eye. The smooth zone area was measured in 400 μm radial segments, and width then calculated.
The overall smooth zone width is 79 ± 22 μm (mean ± S.D.), (n=15), (range = 43 - 115). Quadrant location is found to independently determine smooth zone width (one-way ANOVA, p<0.001). Specifically, the superior quadrant (103 ± 8 μm, n=19) demonstrates significantly wider smooth zone than both the nasal quadrant (71 ± 5 μm, n=19), (p=0.001), and the inferior quadrant (64 ± 5 μm, n=18), (p=0.0001). The combined interaction of age and quadrant location is insignificant (two-way ANOVA, p=0.182). Interestingly, no difference in mean smooth zone width is found between 54-64 year-old "middle-aged" and 77-88 year-old "elderly" patients (two-tailed independent-samples t-test, p=0.484).
The smooth zone is widest superiorly, and thinnest naso-inferiorly, suggesting that glaucoma surgical intervention and device placement could be targeted and administered accordingly. Furthermore, the width of Schwalbe’s line and the smooth zone does not seem to depend on age in adults.
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