Interlacing of Collagen Lamellae in the Midstroma of the Human Cornea

Purpose. To investigate by means of scanning electron microscopy (SEM) the interlacing of collagen lamellae in the midstroma of the human cornea after opening the interlamellar spaces. Material and Methods. For SEM, cells and noncollagenous extracellular matrix were removed with 10% sodium hydroxide. Specimens were dehydrated in a series of graded tertiary butanols, frozen at −24°C and dried in an exsiccator by sublimation of the frozen butanol. Dried corneas were cut vertically with a razor blade, and the interlamellar spaces were exposed by stretching the stroma along its anterior-posterior axis by pulling apart the inner (endothelial) and outer (epithelial) edges. Specimens were sputtered with gold and examined with a Cambridge Stereoscan 90 microscope. Results. The opened interlamellar spaces gave the stroma at the cutting edge the appearance of a polymorphic honeycomb. The stromal openings differed in size, from approximately 10 &mgr;m to over 150 &mgr;m length and up to 80 &mgr;m in height. Adjacent lamellae remained connected at several interconnecting regions, either through an exchange of short merging sublamella or single fibrils. Interlacing lamellae crossed through fissures between the branches of splitting lamellae. Others crossed clefts of neighboring lamellae, and other lamellae tunneled crosswise through a horizontally split lamellae hanging in the inferior branch as in a hammock. Large interweaving zones in which a mixture of several types of interlacing was localized close together could also be found. Conclusion. The current study indicates that interlacing is a distinct and important feature of the human cornea, and it gives new insights into the stromal morphology by demonstrating various types of interlacing that occur between collagen lamellae.