Besides the already mentioned similarities and differences in the cephalopod and vertebrate eye, there are many more left to be said:
- One of the reasons why the higher cephalopod eye can collect light stimuli as well as the vertebrate eye is because both eyes at their maximum density contain over 100,000 photoreceptors per mm2 (Ichikawa et al 1994).
- Since both eyes share a single-lens eye structure, the image that falls on the retina is inverted (Wells 1962, Ichikawa et al. 1994).
Image 13 Display of an Octopus after been threatened by an object bigger than itself. (Image used by permission of Harcourt Education; from Wells, M.J. Brain and Behavior in Cephalopods. Standford University: Stanford. 1962. )