Distribution of Subbasal Nerves in Human Corneas

Abstract

Abstract: : Purpose: Based on analysis of serial frontal sections (18 samples of 1-2 mm² per cornea), we published a 2D scheme of the nerves in the subbasal plexus (SBP) of human corneas (IOVS 1997). At the last ARVO meeting several authors mistook the orientation of the stromal nerves for that of the subbasal nerves. Moreover, this scheme is not complete because subbasal nerves in the apex of confocal images were found to run more often in the 12-6 than in the 9-3 direction. Our aim is to adapt the scheme for the SBP, since refractive surgeons dissect (LASIK) and/or ablate (PRK, LASEK) the majority of the epithelial nerves. Methods: From 5 healthy volunteers the orientation of the subbasal nerves in samples of the apex and mid-periphery at 3, 6, 9 and 12 o’clock position (max. 0.25 mm²) were visualised in both eyes by means of in vivo confocal microscopy. In addition, all serial sections of 7 fresh corneal buttons were re-inspected and 5 corneas stained for whole mount immunocytochemistry (WMI) were compared with the in vivo situation. Results: Nerve fibre bundles (NFBs) in the apex run either in the 6-12, 7-1, 8-2 or 5-11 direction. The direction in the mid-periphery of 3 corneas was similar to that in the apex. However, NFB’s of 2 corneas ran mainly in the 9-3 direction in the apex and at 6 o’clock in the mid-periphery. With WMI we were able to show parallel running fibres in the SBP in samples of 0.37 mm² .On basis of all observations an adapted scheme of the subbasal plexus was made.  

Conclusions: There are no hard data for the most peripheral parts yet. Our current knowledge on the orientation of the nerves in the SBP does not demand a specific location of the hinge of the LASIK-flap. The truth is that most subbasal nerves are disconnected from the stromal nerves. Analysis of serial sections of whole fresh corneal buttons, immuno-stained for nerves, is required to get more insight into the real distribution of epithelial nerves in the human cornea.

Keywords: cornea: epithelium • innervation: sensation • cornea: basic science