Changes in mouse corneal epithelial innervation with age.

PURPOSE We defined the quantitative changes in corneal epithelial nerve fibers during mouse development. METHODS Corneal whole mounts from 36 mice were immunostained with a specific anti-β-III tubulin antibody to label nerve fibers. Epithelial nerve fibers in the whole cornea were scanned and imaged using deconvolution microscopy. Subbasal nerve fiber and nerve terminal densities were calculated based on the length of nerve fibers located in each 1 mm² area of the corneal surface. RESULTS The epithelial nerve terminals and corneal surface areas increased at different rates; therefore, the variations in corneal epithelial nerve terminal density and number were asynchronous. The maximum epithelial nerve terminal density was reached at postnatal day 24, which remained constant until postnatal month 2 and then decreased significantly. However, the epithelial nerve terminal number increased significantly until postnatal month 2 and then subsequently decreased significantly. In contrast to the epithelial nerve terminal, the subbasal nerve fiber density and number increased significantly until postnatal month 2 and then decreased. Since the subbasal nerve vortex was formed at postnatal day 24, its location, morphological appearance, and directionality did not display any further changes with age. CONCLUSIONS The changes in the corneal epithelial nerve fibers can be divided into two stages after birth (day 1 to 2 months and 2-15 months). During the first stage, the corneal epithelial nerve fiber density increased significantly with increasing corneal surface area. During the second stage, the density presented a significant downward trend.