Abstract
Purpose: :
Corneal nerves play an important role in maintaining a healthy corneal surface. The cornea has the highest nerve density and the highest sensitivity among all human tissues, but the detailed innervation network remains unclear. The purpose of this study was to produce a three dimensional map of the entire human corneal nerve architecture and calculate the density of epithelial nerves in different areas of the cornea.
Methods: :
10 fresh human eyeballs from 5 donors (ages 40-63 years old) were obtained from NDRI. After fixation, the whole corneas were steadily mounted in a 24-well plate and kept with their natural curvature when the images were taken. Corneas were stained with mouse monoclonal anti-β-tublin III antibody. Consecutive images were acquired with fluorescence microscope equipped with a digital camera using the MetaVue imaging software in a 2s time-lapse mode. The images recorded at the same position from each cornea were merged together to build a whole view of corneal nerve architecture of both epithelium and stroma. To obtain the transected view of corneal nerves, the same corneas were embedded in OCT, serially sectioned and images were taken.
Results: :
The number of nerves entering the cornea in a radiating pattern were 32.6 ±6.4, (n=10). In the limbal area, 3 to 4 nerve layers could be distinguished. Superficial nerves extending from sub-conjunctival tissues form a dense network within epithelial and anterior stroma. Fine nerve bundles are emerging from the network to innervate the peripheral area of cornea. The tips of the branches, which are predominantly present within the peripheral area with few in the central cornea, penetrate the basement membrane into the epithelia and give place to long bundles. The total numbers of bundles per cornea were 351 ± 53.5 (n=7). These long bundles run like waving lines in the intra-epithelia or sub-epithelia region merged into an area approximately 2mm nasal and 1mm inferior to the central cornea. In the same cornea, the epithelial nerve density differs from the center (59572±4249) to the periphery (37907±5923), with the highest in the merging area (70361±4795). Fine terminals budding from the network innervate the epithelial cells. The superficial epithelial nerve terminal densities in the merging area (142.3 ± 21.1) and in the center (86.4 ± 18.9) are also higher than that in the periphery (61.3 ±12.5). The images of whole transected cornea showed that the epithelial nerve network was located in the intra-epithelial cells not in the sub-basal cells.
Conclusions: :
This is the first study that provides a complete view of the entire human corneal nerve architecture. The findings in this study provide new information in regards to our knowledge of corneal innervation.
Keywords: cornea: basic science • innervation: sensation • immunohistochemistry