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Light Perception - Introduction
In the normal mammalian retina, two spectral cone types, i.e. two visual pigments, can
be found: L-cones with the pigment L-opsin sensitive to middle to long wavelengths; and S-
cones with the pigment S-opsin sensitive to short wavelengths (reviewed in Jacobs 1993).
Twenty percent of the cones found in the Ansell’s mole rat’s eye are exclusively sensitive to
short wavelengths, 10% exclusively to long
wavelengths, and 70% of the cones are
potential dual-pigment photoreceptors
sensitive for both short and long
wavelengths, but with the short-wave-
sensitive pigment dominating markedly
(Peichl et al. 2004). Calculating the
percentages together, 90% of the cones in
the Fukomys anselli retina are sensitive to short
wave light and stand in contrast to the cone
situation in the blind mole-rat’s retina with
no short wave sensitive cones at all (cf.,
Sanyal et al. 1990; Cernuda-Cernuda et al.
2002). Fukomys anselli thus could theoretically
possess dichromatic colour vision, assumed
that the postreceptoral circuitry is given
(Peichl et al. 2004).
However, it is difficult to exactly
determine which wavelength precisely is
absorbed by the visual pigments present in
single photoreceptors. Though the opsin-
specific antibodies identified the opsin family
(S and L), Peichl and colleagues (2004) could
not yield information on the photoreceptor’s
exact spectral tuning, as the applied
antibodies recognize blue as well as UV-
sensitive S-opsins (cf., Szél et al. 2000).
Though most mammalian S-opsins are
sensitive to blue light, it is not improbable
that the S-cones in the Fukomys retina react to
UV-light, as is the case in some rodents
(Jacobs et al. 1991).
Fig. A3 The mole-rat eye. The upper part of
the panel shows a sagittal section of the
Ansell’s mole-rat eye; the diameter is
approximately 2 mm. Picture with kind
permission by L. Peichl. The lower part of the
panel shows a vertical section through the
retina, which shows a normal layer
arrangement and no indications of gross
regression. RPE Retinal Pigment Epithelium,
OS/IS Outer segment/inner segment, ONL
Outer Nuclear Layer, OPL Outer Plexiform
Layer, INL Inner Nuclear Layer, IPL Inner
Plexiform Layer, GCL Ganglion Cell Layer
(from Peichl et al. 2004).
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