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Emmanuel Alabi, Natalie Hutchings, Yunwei Feng, Kostadinka Bizheva, Trefford Simpson; Superior and Inferior Limbal Epithelial and Vascular Structure Characterized Using Ultra-High Resolution Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2590.
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To morphometrically characterize and compare the vessels and the epithelium of the superior and inferior limbal regions.
Cross-sectional images of the human corneo-scleral limbus were acquired with an ultra-high resolution optical coherence tomographer (UHR-OCT) from 20 healthy subjects after manual retraction of the upper and lower eyelid. The UHR-OCT has an axial and lateral resolution in biological tissue of ~3μm and ~10μm, respectively. 3D stacks of OCT images (512 pixels2) were acquired of the transition from cornea to bulbar conjunctiva at the superior and inferior limbal region. The size of the conjunctival and episcleral vessels, the epithelial thickness of the cornea at the limbus and the epithelial thickness at the conjunctiva were quantified (ImageJ, NIH Image). Quantitative differences were analyzed with repeated measure ANOVA.
Figures 1A & B show examples of a median filtered OCT image of the superior and inferior limbus. The outermost low reflective layer corresponds to the epithelium with conjunctival vessels. In the layers beneath, episcleral vessels, scleral tissue and apparent deeper drainage channels are visible. For the upper and lower limbus, mean (±SD) corneal epithelial thickness were 108±11μm and 93±18μm, and mean conjunctival epithelial thickness was 44±10μm and 42±6μm, respectively. The average vessel diameter for the superior episclera and conjunctiva were 34±7μm and 13±1μm. The corresponding diameters for the inferior limbus were 26±8μm and 12±2μm. The corneal epithelium at the limbus was thicker than the conjunctival epithelium (LOC p<0.001), but this was not different between the superior and inferior regions (POS p=0.13). The episcleral vessels were, on average, larger in the superior than the inferior region, whereas the conjunctival vessels were, on average, similar in size (LOC*POS p=0.024).
Superior and inferior bulbar conjunctival and limbal tissue can be imaged and characterized morphometrically using OCT. The primary difference between the superior and inferior limbal morphometry was the episcleral vessel size. This characteristic may be explained as an adaptation to the constant coverage of the superior limbus by the upper eye lid.
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