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been a subject of considerable debate perpetuated by what appear to be
marked differences in opinion as to the type of correlations that might be
drawn between clinically-evident features (in most instances) and the much
greater detail visible in histopathology or electron microscopy.
Some consider the marginal zone to be the natural contact point between
the edge of the lids and the bulbar and corneal surfaces (Kessing 1967, Fatt
1992, Donald et al. 2003, Doughty et al. 2004, Shaw et al. 2009), and attribute
its structural characteristics ( Figs. 2 and 3 ) to it being in frequent pressure-
related frictional motion against these surfaces. Stated another way, this
very narrow zone could be considered as having these features because it
is adapted to playing this specialized role. Others disagree (Bron et al. 2011,
Knop et al. 2011), not only considering that Marx's line cannot be the contact
point but that the special structural features (especially the staining with
lissamine green and rose bengal) are the result of desiccation of the cells.
The latter aspect is not without its merits since, in the normal eye, this part
of the marginal zone would be at the distal edge of the lower tear meniscus
(or lacrimal river or lacrimal lake as it is also sometimes referred to).
Beyond this specialized marginal zone of squamous epithelium, there
is a progressive and gradual transition to the palpebral conjunctiva proper
(Wirtschafter et al. 1999, Knop et al. 2011). The transition includes a slight
depression or partial fold referred to as the marginal sulcus (sometimes
referred to as the ciliary sulcus because of its relative proximity to the
eyelashes).
The eyelid marginal zone is sensitive to touch (a tactile sensitivity)
(McGowan et al. 1994), but is not expected to be as sensitive as the
cornea.
THE PALPEBRAL CONJUNCTIVA INCLUDING THE FORNIX
The Palbebral Conjunctival Epithelium
The palpebral conjunctiva and that covering the fornix are considered to be
'columnar' epithelia that contain goblet cells. This cell layer forms the inner
lining of the eyelids and is normally hidden from view ( Fig. 1A ).
The palpebral conjunctiva is normally coated with mucus. While not
normally visible (i.e. it is transparent), it can be visualized post-mortem
with the use of special chemical fi xatives such as cetylpyridinium chloride
(CPC), which essentially preserve the mucus in its hydrated gel state.
Across the palpebral conjunctiva, at least in rabbits, this fi xed gel layer
can be seen to be very thick in that it is interrupted by large crypt-like
openings (Doughty 1997) ( Fig. 4 ). These clearly extend deep down to the
accessory lacrimal glands (of Wolfring) and are numerous in the rabbit. In
the human eyelid, these glands are more organized into large clusters and
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