Laser-scanning in vivo confocal microscopy reveals two morphologically distinct populations of stromal nerves in normal human corneas

Background: The purpose of this study was to use laser scanning in vivo confocal microscopy to elucidate the location and morphology of stromal nerves in the normal human central cornea. Methods: Analysis was performed via an established database of laser-scanning in vivo confocal microscopy on images of the central cornea of normal subjects. The depth and morphology of the stromal nerves were determined. Results: The population of this study consisted of 99 eyes of 99 healthy subjects (38 male, 61 female). The mean age of the group was 34.7 (SD 13.3, range 13-84) years. Two morphologically different populations of stromal nerves were observed: (1) straight, dichotomous branching nerves; and (2) tortuous nerves with a beaded appearance. The mean recorded depth of straight stromal nerves (186 (SD 66) mm) was significantly deeper than the mean depth of the tortuous stromal nerves (140 (SD 87) mm) (p < 0.001). Conclusions: The current study identified two morphologically distinct stromal nerve populations in the normal human cornea. We hypothesise that the two morphological nerve populations described here may represent functionally heterogeneous nerves. Further research is required to determine if these in fact represent different types of sensory nerves.