In vivo laser confocal microscopy of Bowman's layer of the cornea

Purpose: To investigate in vivo microstructures of Bowman's layer in normal human subjects using a cornea-specific in vivo laser scanning confocal microscope (Heidelberg Retina Tomograph 2 Rostock Cornea Module, HRT2-RCM). Design: Single-center, prospective, observational case series. Participants: Nineteen normal volunteers (10 male, 9 female; mean age, 46.21 +/- 21.7 years [range, 18-77]). Methods: The central and peripheral cornea, specifically the epithelium, Bowman's layer, and its subjacent stroma, were examined using the HRT2-RCM. Main Outcome Measures: Selected images of the corneal layers were evaluated qualitatively for the shape and degree of light reflection of the microstructures. Results: In all subjects, normal epithelial (superficial, wing, basal) cells, subbasal nerve plexus, Bowman's layer, and its subjacent stoma were observed clearly. However, in all subjects, polymorphic structures composed of fibrillar materials with less reflectivity than corneal nerves were observed beneath Bowman's layer. After application of pressure by a Tomo-cap, we observed numerous ridges that protruded into the epithelial basal and wing cell layers. Superficial stromal striae were also observed. These ridges and striae corresponded exactly to the orientation of the fibrous structures located beneath the epithelial cells. Conclusion: We report for the first time, the presence of polymorphic structures composed of fibrillar materials (K-structures) beneath Bowman's layer in normal human subjects, detected by HRT2-RCM. We surmise that these microstructures may correspond to the modified and condensed anterior stromal collagen fibers/lamellae that merge into Bowman's layer and that these fibrillar materials may be responsible for the formation of the anterior corneal mosaic. Further investigation of these microstructures in diseased eyes may provide insights into their pathophysiologic role in Bowman's layer.