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

like the cornea, may exhibit similar spectral properties. In no other species however does keratin
contribute to the optical structures of the eye, as the corneal epithelium of non-spectacled species is
non-keratinized. Keratin, therefore, is a unique material in the layered structure of the eye and thus
may exhibit unique spectral characteristics and provide an extra “degree of freedom” in the evolution
of ocular filtering.
The modest translucency of keratin in most biological structures has resulted in few studies of
its spectral transmittance in the visible and ultraviolet wavelengths (for the sake of convenience, the
term “visible spectrum” will be used to refer to that range visible to humans, that is from
approximately 400 to 750 nm). It has been described for horse hair (Bendit & Ross 1961), human
stratum corneum (Bruls et al. 1984) and for keratin films made from human hair extracts (Reichl et al.
2011), all of which show high transmittance through the visible range but whose spectral profiles differ
slightly in the far UV-A range. Reichl et al. did not report on transmittance of human hair extracts
below 300 nm, but both horse hair and human stratum corneum showed a characteristic peak in the
UV-C at ~254 nm. The only account on the transmissive properties of the spectacle scale alone appears
to have been by Safer et al. (2007) who reported on the transmittance only of the infrared spectrum.
The aim of the research presented here was primarily to document the spectral transmittance of
shed spectacle scales of snakes and geckos to gauge similarity with known keratin spectra and to
determine whether any observed variation might be accounted for by evolutionary relationships.
Because of the role played by the spectacle in mechanical protection of the eye (Walls 1942), the
thickness of the scales was also considered to determine if and how trade-offs might occur in balancing
thickness and spectral transmittance.
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