Scanning electron microscopy of normal human corneal epithelium obtained by scraping-off in vivo

Quantitative Analysis of Ring-Shaped (Crater-Like) Features at the Tear Film–Epithelial Interface of the Rabbit Cornea as Assessed by Scanning Electron Microscopy

PURPOSE

To develop a method for the quantitative analyses of the ring-shaped features usually observed on the surface of mammalian corneal epithelial cells.

METHODS

The corneas of 10 young adult female albino rabbits were prepared for scanning electron microscopy (SEM) by fixation in 2% glutaraldehyde in 80 mM cacodylate buffer (pH 7.2 to 7.4, 320 to 340 mOsm/kg) and single images taken at 1000x of the central region of the corneal epithelial surface. On enlarged prints at 5000x final magnification, cell-cell borders were marked as were the outlines of the ring-shaped features. Cell areas and the dimensions of the ring-shaped features were measured and the cell characteristics in terms of electron reflex (light, medium, and dark) as well as the number of apices (sides) also noted.

RESULTS

The ring-shaped features had an overall density of 2.5/100 microm2, or an average of 6.5/cell. With the corneal epithelial cells being small and light in appearance (median area 36 microm2), medium in size and appearance (median area 151 microm2), or larger and darker (median area 476 microm2), the number of features/cell was very strongly associated with both the cell type (p < 0.001) and the cell area (p < 0.001). The ring-shaped features could be between 0.65 and 5.5 microm in diameter, but sizes more than 3 microm were most unusual. Ring-shaped features of light cells were smallest (median diameter 1.35 microm), slightly larger on medium cells (1.55 microm), and largest on the dark cells (1.90 microm).

CONCLUSIONS

The ring-like features seen on SEM photomicrographs of rabbits (also known as craters or holes) are reproducible in terms of their overall density per unit surface area as well as their diameter. Such methods should be useful for objective analysis of these features after various treatments of the ocular surface.

Morphometric analysis of the surface cells of rabbit corneal epithelium by scanning electron microscopy

The corneal surface of female New Zealand white rabbits (1.9-2.6 kg) was examined at x500 magnification by scanning electron microscopy. A total of 112 micrographs, taken as sequential sets from the center to the edge of the corneal surface from 8 different animals, was analyzed using a digitizer pad. Each cell was identified by the number of immediately bordering cells and by the nature of its electron reflex (light, medium, dark). Analysis of areas of the cells by number of bordering cells (number of cell sides) reveals a wide range of areas and skewed distributions especially when the number of sides is 5 or less. Overall, the cell-surface area increases as the number of cell sides increases. However, analyses of the mean surface areas for cells with different numbers of sides and additionally grouped by electron reflex suggests the existence of three separate populations of cells at the corneal surface. The possible etiology and dynamics of this complex cell mosaic are discussed in relation to circadian rhythms and to resurfacing of the cornea following mechanical trauma, ultraviolet radiation, and toxic chemical exposure.

Mucus alteration and eye dryness. A possible relationship

From a very early phase we studied 15 patients suffering from a dry-eye condition ant associated to systemic diseases. Conjunctival biopsies were studied in Transmission (TEM) and Scanning (SEM) electron microscopy. Moreover, the lectin-gold cytochemistry at ultrastructural level was applied to investigate the distribution of some glycosidic receptors produced by both the goblet cells and the vesicles belonging to the Second Mucus System (SMS). No evidence of epithelial stratification and only a decrease in the goblet cell population was observed. The SMS vesicles and the superficial cell microvilli did not appear greatly reduced in number. A difference in the mucus composition in terms of content of glycosidic residues was detected in dry-eye patients compared to the normal subjects. The role of the mucus produced by both the goblet cells and the SMS vesicles in debated. A possible correlation between the alteration of the mucus content and the failure of the tear film stability is proposed. On the basis of these data, a new therapeutic approach for eye dryness is suggested.

The interaction between Neisseria gonorrhoeae and the human cornea in organ culture. An electron microscopic study

Explants of human corneas in organ culture were used to study the interaction between Neisseria gonorrhoeae and human corneal epithelium at an ultrastructural level. scanning electron microscopy revealed that infection of the corneal explants with N. gonorrhoeae resulted in a rapid adherence of the bacteria to the cell surface. This attachment was probably mediated by pili since only piliated strains were able to adhere to the cells. Upon attachment the bacteria appeared to become engulfed by the epithelial cells. Transmission electron microscopy revealed gonococci apparently lying within vacuoles inside the cells within 1 h after inoculation of the bacteria. At prolonged infection (8-24 h), the thickness of the epithelium was found to be considerably reduced. This thinning of the cornea was probably caused by a continuous desquamation of infected cells. Taken together, the present data demonstrate that Neisseria gonorrhoeae is able to adhere and penetrate into intact corneal epithelium and furthermore indicate that human cornea explants in organ culture are a useful model in studies of bacterial-epithelial cell interaction.