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and the overall matrix is populated by numerous cells (Doughty et al. 2001b,
Mathew et al. 2008).
The type I collagen forms the basis of small diameter fi brils (see later)
which in turn, are arranged in a highly organized pattern in fl attened bundles
called lamellae; fl attened cells, called keratocytes, are usually found between
the lamellae (see later). In more recent studies on human corneas, the more
anterior stromal lamellae have been reported to have average thickness
values of 1.29 ± 0.23 µm, while the posterior lamellae were thicker with an
average of 2.92 ± 1.54 µm; the overall average lamella thickness value was
1.66 ± 0.11 µm (Takahashi et al. 1990). In another study, it was noted simply
that the more anterior lamellae varied in thickness from about 0.2 to 1.2 µm
while a range from 0.2 to 2.5 µm was found in the posterior stroma (Komai
and Ushiki 1991). Similar ranges of values have been reported for a variety
of animal corneas as well (Doughty et al. 2001b).
When viewed by transmission electron microscopy at very high
magnifi cation, the collagen fi brils within the stromal lamellae of the normal
mammalian cornea are all of very similar diameter and are relatively
uniformly spaced. The clarity of the collagen fi brils and the fi ner details
of the surface of the individual fi brils probably depend on the quality of
the post-mortem tissue. While it is likely that images of the type shown in
Fig. 15A can be fairly easily obtained from very recent post-mortem corneal
samples (Doughty and Bergmanson 2004b), images of the type shown in
Fig. 15B will more likely be obtained from an eyebank sample that had been
stored for a few days (Bergmanson and Doughty 2005).
As shown in Fig. 15 , the stromal fi brils are specially arranged so that
there is a certain space occupied by the fi brils. For posterior corneal stroma
Figure 15 Very high magnifi cation transmission electron microscopy images of rabbit (A) and
human (B) stroma to show fi brils, and (C) the distribution of fi bril diameters in the rabbit. (A)
and (B) from Bergmanson and Doughty 2005, copyright Lippincott-Williams & Wilkins, (C)
from Doughty and Bergmanson 2005, copyright Elsevier.
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