The three-dimensional microanatomy of the rabbit and human cornea. A chemical and mechanical microdissection-SEM approach

The three-dimensional (3D) microanatomy of the cornea is the major determin ant of its optical and mechanical properties. Scanning electron microscopy (SEM) is the most commonly used method to obtain information on the overall 3D microanatomy of organs. However, SEM has not been successful in reveali ng the 3D microanatomy of the cornea, because the interior of the cornea is too compact to be explored by the electron beam. In this study, the 3D org anisation of the cells and extracellular materials of human and rabbit corn eas was examined after exposure by HCl and NaOH digestion, and by microdiss ection by the adhesive tape method. In the cornea of both species, all epit helial cells exhibited microplicae regardless of their location. This raise s doubts about the tear film-holding role assigned to the microplicae of th e superficial cells. Human and rabbit corneas differed in the collagen fibr e patterns of the epithelial basement membranes. The 3D organisation of the stromal lamellae was similar in both species. In humans and rabbits, the k eratocytes showed similar 3D features. However, the surface of human kerato cytes located near Descemet's membrane exhibited small fenestrations that w ere not present in the rabbit keratocytes. The pattern of keratocyte innerv ation by the stromal neural plexus and 3D keratocyte microanatomy confirms that keratocytes form a large intercommunicating network within the corneal stroma. Two morphologically discrete subpopulations of keratocytes located at different stromal levels were identified in both human and rabbit corne as, suggesting that keratocytes are not functionally homogeneous. In additi on, the density of the stromal neural plexus appeared to be greater in rabb its than in humans. Clear differences between human and rabbit corneas were observed in the collagen arrangement in Descemet's membrane, which may ref lect their different biomechanical requirements.