Healthcare and Medicine Reference
Figure 10 Transmission electron micrograph to show part of a large conjunctival lymphatic
vessel with irregular endothelial lining (from Doughty and Bergmanson 2003), copyright
American Optometric Association.
form of an overlap, without obvious cell-cell junctional complexes (Iwamoto
and Smelser 1965, Nichols 1996, Cursiefen et al. 2002). Examination of
the outer edger edge of lymphatic vessels reveals no obvious supportive
cells (pericytes), but there are characteristic discrete bundles of collagen
fi brils that appear to serve the role of anchoring the lymphatic vessels to
surrounding connective tissue.
The lymphatic system under the bulbar conjunctiva contains valve-like
structures (Grüntzig et al. 1990), which are presumed to control the net fl ow.
This is generally in a temporal direction towards the lateral extremes of the
eyelids (to the parotid node) with some via a medial route (leading to the
submandibular lymph nodes). Any abrupt change (reduction) in the fl ow
(perhaps as a result of a special regulation of these valves) can result in
dramatic changes in the fl uid content of the sub-epithelial parenchyma (e.g.
manifest as chemosis). Detailed information of the location and mechanism
of control of these valves has yet to be described.
THE CORNEAL EXTERNAL APPEARANCE AND
External Dimensions, Curvature and Surface Appearance
As based on measures on post-mortem human eyes, the corneal area is
approximately 1/10th of the surface area of the globe (Olsen et al. 1998)
and only about 1/15th of the surface area of the conjunctiva (Watsky et al.
1988). When viewed from the outside, the cornea has a certain diameter,