The head and eye of the sand lance, Limnichthyes fasciatus‐a field emission scanning electron microscopy study

Abstract

Background: The anterior surface of the cornea is an important component in retinal image formation. In mammals, the anterior cell surface is covered with numerous microvilli but in fish there are microplicae. However, there is little else known about the corneal surface of teleosts.

Methods: The cornea, conjunctiva and skin of the head of the sandlance, Limnichthyes fasciatus, a small teleost found off the coast of Australia, were examined using field emission scanning electron microscopy.

Results: The central corneal surface has an epithelial cell density of 21,475 ± 4,750 cells per mm² while in the periphery the cell density is less (14,785 ± 3,630 cells per mm²). The central and peripheral epithelial cells have a dense pattern of microplicae, around 135 nm in width and many microns in length. There are no craters in the cell surface but holes or pits around 1.6 μm in diameter are present at 10 to 15 per cent of junctions where three surface cells meet in the peripheral cornea. The cells of the conjunctiva, nose and skin of the head also have microplicae, the patterns of which show similarities to those of the cornea. Some nasal cells are partially covered with a material, possibly mucus.

Conclusion: The microplical pattern found on the cornea of the sandlance is similar but not identical to that seen in other teleosts. The pattern found on the conjunctiva and scales of the head is also similar, although these structures show a lesser cell density and a greater microplical separation than the central cornea. These changes may be associated with differences in cell function. (ClinExp Optom 1997; 80: 4: 133–138)

Key words:

• conjunctiva
• cornea
• corneal craters
• epithelium
• fish
• microplicae