Computerised morphometry and a double stain technique were utilised
to
examine the corneal nerves in
whole mounts. This novel stain combines the nonspecific acetylcholinesterase
(NsAchE) and gold chloride
(AuCl) procedures to enhance staining contrast and facilitate computerised
detection of corneal nerves.
Fresh rat corneas were dissected, and the Descemet's
membrane-endothelium complex was removed. Then
the corneas were fixed in 4% paraformaldehyde with 50 mm
Na-K phosphate buffer (pH 7.2) and 8%
sucrose for 30 min. They were rinsed and stained singly with
NsAchE or AuCl, or were double stained using
NsAchE followed by AuCl. Between NsAchE and AuCl staining the corneas were
stored frozen in OCT
compound at −70°C. Flat mounts of whole corneas were photographed
before and after the second
staining. Measurable stromal innervation density (mean±S.D.)
in
age-matched corneas stained with AuCl
(3.90±0.36 mm/mm2) was not significantly different
from that of NsAchE stained corneas. However, double
staining compared with NsAchE staining of the same corneas revealed a
48±27% increase in demonstrable
innervation density of the subepithelial nerve plexus (7.95±0.86
mm/mm2 vs 5.52±1.31 mm/mm2,
respectively). Improved visualisation of epithelial nerves and their fine
ramifications (leashes) was also
obtained by double staining. This novel combination of 2 procedures enhances
the detection of corneal
nerves for analysis by computerised morphometry and provides a more
representative estimate of total corneal innervation density.