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Jan P G Bergmanson, Carmen L Mosqueda, Alan R Burns; Human Stromal Lamellar Morphology and Its Relationship to Central to Peripheral Thickness Change. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2366.
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© 2017 Association for Research in Vision and Ophthalmology.
The human cornea is thicker peripherally than centrally, but is this due to a greater number of lamellae in the peripheral cornea or an increase in lamellar thickness, or both? The purpose of this study was to determine the total number of lamellae present and the average lamellar thickness in the anterior, middle and posterior stroma, both in the central and extreme peripheral normal cornea.
Three eye bank corneas were processed and examined with a Tecnai G2 12 Twin transmission electron microscope (FEI Company Hillsboro, OR) operating at 100 kV and magnified at 4200X. Montages of overlapping images from epithelium to endothelium were assembled for each cornea for extreme periphery and central regions. Lamellae on each montage were marked and counted using an established protocol. The stroma was divided into anterior, mid and posterior segments. Data were expressed as means ± SD and differences assessed using Analysis of Variance (ANOVA) and Tukey post-hoc tests with significance set at P ≤ 0.05.
The central/peripheral lamellar counts for each cornea (260/260; 231/235; 247/257) were remarkably similar. As the lamellae approach the central region they were frequently observed to branch. However, peripheral posterior lamellae were on average twice as thick as those in the central cornea (3.2 ± 0.4 and 1.6 ± 0.3 µm, respectively), with some lamellae reaching 10 µm in thickness. Anterior lamellae were thinner than mid-stromal lamellae, but only at the periphery.
The human cornea is thicker in the periphery not because it has more lamellae but because it has thicker posterior lamellae. While lamellar branching is common, the total number of lamellae (~250) does not increase centrally. Therefore, some lamellae must stop short of crossing the cornea. Given that keratoconic cornea has considerably more lamellae (~350) at the cone apex, it will be important to establish whether this increase is also present peripherally.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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