A range of distinctive visual designs are described for fish requiring extreme
sensitivity to benefit from vision in the near-dark. Enhancements include extremely
long pigmented segments in rod cells; retinas backed with reflecting tapeta to return
unabsorbed light back through them; wrapping of bundles of rods reporting to a single
ganglion cell in reflective tube cells; and extremely long visual integration intervals
before ganglion discharge to the optic nerve. Those modifications increase sensitivity
but consistently at the cost of spatial or temporal resolution. Possibly, it is more
important to see something against the very dim background, than for the scene (or
flashes) to be sharply defined.
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