Purpose: To use transmission electron microscopy (TEM) to investigate further the ultrastructural details of the collagen fibrils linking the anterior limiting lamina (ALL; Bowman's membrane) of the human cornea to the anterior stromal lamellae.
Methods: Six disease-free corneas from donors aged 42 to 82 years were fixed (2% glutaraldehyde in 80 mM sodium cacodylate) and processed for TEM within 72 hours postmortem. A series of overlapping images, at 10,204x magnification, of the central corneal ALL-stroma interface were assembled. The features of the terminal ends of fibril bundles at the interface with the anterior stroma were quantitatively assessed.
Results: TEM revealed apparently terminating anterior stromal fibril bundles adjacent to the ALL. These terminating lamellae (7.8 per 100 mum) were embedded in an electron-dense material within the surrounding stromal matrix and were termed electron-dense formations (EDFs). The mean width of these stromal features was 1.6 mum. At intervals, anterior stromal lamellae approached the ALL and, in a shallow manner, inserted into the ALL. Such projections (5.4 per 100 mum) into the ALL were, on average, less than 1 mum. Numerous fibrils (29.8 per 100 mum) extended from the ALL into the stroma with a mean length of 0.8 mum.
Conclusions: The interface the ALL forms with the anterior stroma is complex, and TEM revealed at least three different types of fibrillar arrangements, which may serve optical requirements rather than provide a structural function.