Three-dimensional analysis of collagen lamellae in the anterior stroma of the human cornea visualized by second harmonic generation imaging microscopy

The structure of collagen lamellae in the anterior stroma of the human cornea is thought to be an important determinant of corneal rigidity. The three-dimensional structure of such collagen lamellae in normal human corneas was examined. The anterior portion of 27 normal human corneas was obtained from donor tissue for Descemet's stripping automated endothelial keratoplasty (DSAEK) surgery, and blocks (∼3-mm square) of the central cornea were examined by second harmonic generation (SHG) imaging microscopy. Each cornea was scanned from the surface of Bowman's layer to a depth of 150 μm, and SHG forward signals were collected. The angles of collagen lamellae immediately below to a depth of 30 μm below Bowman's layer (sutural lamellae) as well as of those at a depth of 50 or 100 μm were measured. The density and width of sutural lamellae were also evaluated. Collagen lamellae in the anterior stroma were evenly distributed and randomly oriented. The angle of sutural lamellae relative to Bowman's layer was 19.19 ± 4.34° (mean ± SD). The angles of collagen lamellae at depths of 50 or 100 μm were 8.91 ± 2.91 and 6.91 ± 2.11°, respectively. The density of sutural lamellae was 910.0 ± 480.4/mm(2), and their width was 13.14 ± 5.03 and 7.11 ± 3.00 μm in the region immediately beneath and 30 μm below Bowman's layer, respectively. Collagen lamellae in the anterior stroma of the normal human cornea are interwoven in three dimensions and adhere densely to Bowman's layer. This structure may contribute to the rigidity and curvature of the anterior portion of the cornea.