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Ophthalmology

Ultrastructure of the posterior corneal stroma.


PMID 25458195

Abstract

To reinvestigate the ultrastructure of the posterior stroma of the human cornea and to correlate the findings with the stromal behavior after big-bubble creation. Observational consecutive 3-center case series. Fresh corneoscleral buttons from human donors (n = 19) and organ-cultured corneoscleral buttons (n = 10) obtained after Descemet's membrane endothelial keratoplasty. Corneal specimens were divided into central (3 mm), mid peripheral (8 mm), and peripheral parts by trephination and processed for transmission electron microscopic and immunohistochemical analyses. A big bubble was created by air injection into the stroma of organ-cultured corneas before fixation. The distance of keratocytes to Descemet's membrane, number of collagen lamellae between keratocytes and Descemet's membrane, diameter and arrangement of collagen fibrils, thickness of stromal lamella created by air injection, and immunopositivity for collagen types III, IV, and VI. Stromal keratocytes were observed at variable distances from Descemet's membrane, increasing from 1.5 to 12 μm (mean, 4.97±2.19 μm) in the central, 3.5 to 14 μm (mean, 8.03±2.47 μm) in the midperipheral, and 4.5 to 18 μm (mean, 9.77±2.90 μm) in the peripheral regions. The differences in mean distances were significant (P < 0.0001). The number of collagen lamellae between Descemet's membrane and most posterior keratocytes varied from 2 to 10 and the diameter of collagen fibrils averaged 23.5±1.8 nm and corresponded with that of the remaining stroma. A thin layer (0.5-1.0 μm thick) of randomly arranged, unaligned collagen fibers, which was positive for collagen types III and VI, was observed at the Descemet-stroma interface. The residual stromal sheet separated by air injection in 8 of 10 donor corneas varied in thickness from 4.5 to 27.5 μm, even within individual corneas (≤3-fold), and was composed of 5 to 11 collagen lamellae that revealed keratocytes on their anterior surface and in between. Barring an anchoring zone of interwoven collagen fibers at the Descemet-stroma interface, the findings did not provide any evidence for the existence of a distinctive acellular pre-Descemet's stromal layer in the human cornea. The intrastromal cleavage plane after pneumodissection seems to be nonreproducibly determined by the intraindividually and interindividually variable distances of keratocytes to Descemet's membrane.