Chapter 1, The Reptilian Spectacle - UWSpace - University of ...

and spectacle via diffusion through the aqueous or by the limbal blood supply via diffusion through the
subspectacle fluid.
Though spectacle vessels are present in all snakes and likely in all spectacled squamate (see
Chapter 1), it is comparatively unusual, but not unknown, for blood vessels to be present in the optical
path of the anterior segment of other vertebrates’ eyes. It can occur, for example, among mammals and
birds in the form of corneal neovascularization associated with an underlying pathology (Lee et al.
1998; Chang et al. 2001; Williams & Whitaker 1994; Maggs et al. 2008). The Florida manatee,
Trichechus manatus latirostris, exhibits non-pathological corneal vascularity (Harper et al. 2005), and
although the anatomical distribution of the manatee’s corneal vessel network has been described in
great detail, the author is unaware of any work describing its corneal blood flow dynamics. Given the
comparatively low visual acuity of these animals (Bauer et al. 2003), the evolution of compensatory
blood flow mechanisms seems unlikely.
Further research will be necessary to determine if the results described here hold true for other
species of snakes and squamates with spectacles or windowed eyelids, as well as other vertebrates that
possess other forms of spectacle (eg. fish) and transparent eyelids (eg. frogs and turtles).
As integument, the reptilian spectacle, being adapted to the ocular need of tissue transparency,
offers an unprecedented value as a means to study cutaneous vascular physiology. In combination with
their large erythrocytes that are relatively easier to image than those of mammals, snakes may be an
excellent model animal for studying peripheral vascular dynamics. As discussed above, a
comparatively low proportion of spectacle blood flow was noticed in early trials when a snake was
moved from a warm terrarium to a lower ambient temperature. The imaging techniques described here
could be of significant utility in studying cutaneous blood flow dynamics during thermoregulation, or
for any other purpose where the quantification of cutaneous vascular flow is called for.
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