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J. H. Mathew, J. D. Goosey, J. P. G. Bergmanson; Is Stromal Thinning in Keratoconus Explained by Lamellar Dropout?. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3535.
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The clinical presentation of keratoconus (Kc) involves corneal stromal thinning and ectasia. The purpose of this study was to count stromal lamellae in the Kc cornea to determine whether corneal thinning can be explained by a lamellar dropout.
Five surgically removed Kc corneal buttons were immediately preserved and processed for transmission electron microscopy using an established corneal protocol, ensuring minimal tissue shrinkage and distortion. A sequence of overlapping digital micrographs of the full apical cone thickness was taken at 860x microscope magnification. A seamless montage, created using PanaVue ImageAssembler 3 software, was printed (Roland FJ-52) at a final magnification of 5000x. The number of lamellae were counted using an established set of criteria for identifying individual lamellae.
Among the corneas examined, three had distinctly similar histopathology and were considered ‘typical’ Kc. The other two cases, hydrops (H) and extreme thinning (ET), were considered individually. The ‘typical’ Kc cornea had, on average, 372.7 (SD: +15.9) lamellae, while the H and ET corneas showed 308 and 109 lamellae respectively. All corneas showed clear ultrastructural evidence of lamellar fragmentation into smaller units and a loss of interweaving anterior lamellae.
Our earlier research demonstrated that Kc leads to a loss of anterior limiting lamina over significant areas, while the current work indicated that the interweaving anterior stromal lamellae are also removed in the disease process, explaining the corneal thinning. Interestingly, all corneas exhibited a dramatic increase in stromal lamellae compared to our previous research on normal human corneas showing 242 lamellae on average. A large number of lamellae less than 1um thick were consistently encountered in all the corneas suggesting that fragmentation of the lamellae across the entire thickness is a pathophysiological feature of Kc. The anterior loss of stromal tissue together with a generalized fragmentation of lamellae may be dominant factors in corneal ectasia. Kc is a complex corneal pathology, and its associated stromal thinning cannot be explained by a simple lamellar count.
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