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J. Tukler Henriksson, A. McDermott, J. P. G. Bergmanson; Structural Explanation for Central to Peripheral Thickness Variation in the Mouse Cornea. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3933.
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As has been described for other mammals, including humans, the mouse cornea varies in thickness across its diameter. The purpose of the present study was to explain, on a structural basis, this thickness difference, which can amount to a 58 % decrease from center to periphery in the mouse cornea.
Six mice (three C57BL/6 and three 129/SVJ) were euthanized and 2 % glutaraldehyde fixative immediately applied to the cornea. The eyes were enucleated, immersed in fixative and the corneas processed for histology. Thick sections were stained with 1 % toluidine blue and viewed at 200X with an Olympus BX51 light microscope. Keratocytes were counted vertically at the center and at the peripheral limit of the cornea, defined histologically as immediately central to limbal loops and central to the anterior edge of the trabecular meshwork. The central keratocyte count was performed, 880-1150 um from the peripheral count. The number of layers of epithelial cells was also counted in the central and peripheral cornea.
Both strains showed a statistically significant (P < 0.001) decrease in the number of keratocytes in the peripheral compared to central cornea. The 129/SVJ mouse had 15.45 ± 0.94 keratocytes in the center versus 9.78 ± 0.59 in the periphery, and the C57BL/6 mouse had 13.62 ± 1.22 keratocytes in the central cornea versus 8.39 ± 0.68 in the periphery. In both strains the epithelium of the peripheral cornea had on average one less layer of cells (range 6-8) compared to the central cornea (range 8-10).
Keratocytes are predominantly positioned between stromal lamellae and therefore the number of keratocytes present in an anterior-posterior orientation provides an indication of the number of lamellae forming the stroma at a particular corneal locus. Thus, it can be concluded from this study that the peripheral thinning of the mouse cornea, is explained primarily by a decreased number of stromal lamellae and to a lesser degree a reduction in epithelial layers. However some compacting of the tissue towards the periphery may also occur. Thickness differences in the human cornea may have a similar explanation.
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