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

hydration state (van Doorn, unpubl. obs.), so they are not dependent on the precise balancing of water
flux as is the cornea. Campbell et al.‘s (1999) work on the surface ultrastructure of a python’s scales,
described earlier, did show that the surface of the spectacle scale differs from others in having features
which are less likely to cause optical scatter. The specific complement of keratins and their
arrangement may also play a role in transparency. In chapter 4 of this thesis, results of investigations
on the biochemical composition of spectacle scales will be presented, which is hoped can provide a
foundation for further research to determine the relationship between scale composition and spectral
transmittance.
The even and parallel boundaries between adjacent layers of the spectacle is unquestionably
essential to achieving transparency. Because of the large difference between refractive indices of
keratin and dermal tissues (nkeratin - ndermis ≥ 0.13), it is essential that the boundaries between the dermis
and epidermis/stratum corneum remain as even and as parallel as possible to minimize random scatter
and reflection of incident light. This can be understood by considering Figure 1-13.
Figure 1-13. Diagram of the effects of uneven surface in adjoining layers with different
refractive indices. In contrast with an optical system with smooth surfaces (B), the system with an
uneven boundary exhibits scatter of the incident illumination (A). (diagram by K. van Doorn)
1.4 Physiology of the Spectacle
The barrier properties of the reptile integument to cutaneous fluid flux and respiration have been the
subject of some research (Lillywhite and Maderson 1982; Feder and Burggren 1985). Unfortunately no
work has been published to my knowledge on the particular characteristics of the spectacle.
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