A number of cephalopods particularly the squids and octopuses, and potentially cuttlefish, have eyes that can distinguish the orientation of polarized light. This sensitivity is due to the orthogonal organization of neighboring photo-receptors.

In comparison, the vertebrate eye is normally insensitive to polarization differences because visual pigment in rods and cones is arrayed semi-randomly, and is thus equally sensitive to any orientation of the e-vector axis of the light.

In cephalopods, due to their orthogonal organization, the visual pigment molecules in their eyes have the highest light absorption when aligned properly with the light e-vector axis, allowing sensitivity to differences in polarization.

The precise function of this ability has not been proven, but is hypothesized to be for prey detection, navigation, and possibly communication among the color-changing cephalopods

Is it also true that a cephalopod eye has no blind spot because the optic nerve linking the eye and the brain starts behind the retina rather than directly on it?

Dear Dr. Mark

Cephalopods have a well developed nervous system. They can make out focused images (with many focal points helping them to detect movements wonderfully) and can see plane polarized light. In a latest study, D-Asp (D-aspartate) was found in the retina of the cephalopods (e.g. Sepia officinalis, Loligo vulgaris and Octopus vulgaris) playing important role in vision. There are two eye types found in this taxon: (1) pinhole type eye that opens to the environment and is in direct contact with the water and lacks a cornea or a lens, and (2) camera-type eye, similar to those of vertebrates, containing an iris, a pupil, a circular lens, vitreous cavity and photoreceptors forming a retina. Further, there is no blind spot in the cephalopod eye and except firefly squid, Watasenia scintillans, all other cephalopods are color blind.

The likeness between the eye-type in cephalopods (camera type) and the vertebrates is an example of parallel evolution. A conserved gene sequence governs eye development in both vertebrate and invertebrate lineages. It is just that the organogenesis of the eye is somewhat different in the cephalopods than that of the vertebrates.

These literature may be of some help to you:

1. http://hermes.mbl.edu/mrc/hanlon/pdfs/mathger_polariz09.pdf

2. http://hermes.mbl.edu/mrc/hanlon/pdfs/Hanlon%20etal%20CephAdapCamou%20CUPbookChap%202011.pdf

Best

Dola.

Its true that the cephalopod eye has no blind spot.

In vertebrate eyes, the nerve fibers route before the retina, blocking some light and creating a blind spot where the fibers pass through the retina and out of the eye. In cephalopod eyes, the nerve fibers route behind the retina, and do not block light or disrupt the retina thus the vertebrate blind spot is notably absent in the cephalopod eye.