Abstract
Abstract: :
Purpose: Predominately, literature suggests that stromal lamellae extend, uninterrupted, limbus to limbus. The purpose was to seek evidence to prove or disprove this hypothesis and to define the stromal–anterior limiting lamina (ALL) interface. An understanding of the normal stromal layout is necessary before we can explain, and one day treat, stromal diseases such as keratoconus and pellucid marginal degeneration. Methods: Six normal eyebank harvested corneas from six individuals were prepared for transmission electron microscopy according to an established protocol. Panoramic photographic montages of central cornea at X10,204 were assembled using a Jeol 100C operating at 60KV. This wide angle view was surveyed for evidence of anterior stromal lamellar continuity and stromal–ALL interface interactions. Results: The complex lamellar pattern at the interface provided few clues in favor of a strictly limbus to limbus lamellar bridge. Instead, anterior lamellae in this location branched into successively smaller units while moving anteriorly and terminating parallel to the ALL. Stromal lamellar projections into ALL were infrequent and shallow and never projected further than 1.56um (avg: 0.53um). Short fibrous extensions from ALL projecting into stroma averaged 0.81um. Adjacent to the interface were areas of increased electron–density in the stromal matrix around apparently terminating lamellae. These discrete, granular, local electron–dense formations (EDF's), possibly synthesized by anterior keratocytes, were on average 1.54um in diameter and were located within 2.64um of ALL. Conclusions: Evidence did not support an uninterrupted limbus to limbus bridging of anterior stromal lamellae, nor were there signs of distinct lamellar insertions into ALL. Only superficial and limited mingling between the two layers was seen. Instead, these lamellae seemed to terminate while embedding into an electron–dense matrix which may be providing anchorage for collagen fibers. The previously, undocumented sub–ALL EDF's may have a function in facilitating adhesion between the two layers. Whether stromal lamellar discontinuity evolved to serve structural or optical needs, and if it is of consequence in stromal disease, has yet to be determined.
Keywords: cornea: stroma and keratocytes • keratoconus