The effect of age on the corneal subbasal nerve plexus

Purpose: To measure subbasal nerve density and orientation in normal human corneas across a broad age range. Methods: Sixty-five normal corneas of 65 subjects were examined by using tandem scanning confocal microscopy. Ages of subjects ranged from 15 to 79 years (mean 46 19 years), with 5 subjects from each hemidecade. Subbasal nerve fiber bundles appeared as bright, well-defined linear structures in confocal images of the central cornea. Images from 3 to 8 scans per eye (mean 4.6 +/- 1.8 scans) were randomly presented to a masked observer for analysis. The mean subbasal nerve density (total nerve length [mu m] within a confocal image [area = 0.166 mm(2)]), the mean nerve number per confocal scan, and the mean nerve orientation were determined by using a custom software program. Correlations between age and nerve density and age and nerve orientation were assessed by using Pearson correlation coefficients. Results: The subbasal nerve plexus was visible in the central cornea of all subjects. The mean subbasal nerve density was 8404 +/- 2012 mu m/mm(2) (range 4735 to 14,018 mu m/mm(2)). The mean subbasal nerve number was 4.6 +/- 1.6 nerves (range 1 o 8 nerves). The mean subbasal nerve orientation was 94 +/- 16 degrees (range 58 to 146 degrees). There was no correlation between age and subbasal nerve density (r = 0.21, P = 0.09) or between age and subbasal nerve orientation (r = -0.19, P = 0.12). Conclusion: The density and orientation of the subbasal nerve plexus in the central human cornea does not change with age.