Cephalopod eye

Vertebrate

Octopus

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. In cephalopod eyes, the nerve fibers route behind the retina, and do not block light or disrupt the retina. 4 denotes the vertebrate blind spot. In vertebrates, 1 denotes the retina and 2 the nerve fibers, whereas in cephalopods, it is opposite. 3 is the optic nerve.

Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions.^[1] They have a camera-type eye, which consists of a lens projecting an image onto a retina. Unlike the vertebrate camera eye, the cephalopods' form as invaginations of the body surface (rather than outgrowths of the brain), and consequently they lack a cornea. Unlike the vertebrate eye, a cephalopod eye is focused through movement, much like the lens of a camera or telescope, rather than changing shape as the lens in the human eye does. The eye is approximately spherical, as is the lens, which is fully internal.^[2]

The crystalins used in the lens appear to have developed independently from vertebrate crystalins, suggesting a homoplasious origin of the lens.^[3]

Most cephalopods possess complex extraocular muscle systems that allow for very fine control over the gross positioning of the eyes. Octopuses possess an autonomic response that maintains the orientation of their pupils such that they are always horizontal.^[1]

Polarized light

It has been documented that several types of cephalopods, most notably squid 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 photoreceptors. To illustrate, the vertebrate eye is normally insensitive to polarization differences because visual pigment in rods and cones is arrayed semi-randomly, and is thereby equally sensitive to any orientation of the e-vector axis of the light. Because of their orthogonal organization, the visual pigment molecules in cephalopod eyes have the highest light absorption when aligned properly with the light e-vector axis, allowing sensitivity to differences in polarization.^[4] 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.^[4][5]

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  Eye of Bathyteuthis sp.

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  Octopus (Octopus vulgaris) eye

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  Squid eye

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  Cuttlefish eye

• 

  Nautilus (Nautilus pompilius) eye

See also

Book: Cephalopoda

• Mollusc eye
• Octopus sensation
• Squid nervous system
• Evolution of the eye

References

v t e Cephalopod anatomy Shell Shell types External shells: Ammonoid shell Argonautid eggcase Nautiloid shell Orthocone Internal shells: Belemnoid guard Cirrate shell Cuttlebone Gladius (pen) Spirula shell Stylet External features Aperture Apex Callus Lirae Periostracum Sculpture Spire Sutures Umbilicus Internal features Body chamber Camerae Nacre Phragmocone Septa Siphuncle Whorls Mantle External anatomy Dermal structures Fins (wings) Flotation devices ("secondary fins") Mantle locking-apparatus Tail Internal anatomy Branchial hearts Ctenidia (gills) Hepatopancreas (digestive gland) Ink sac and ink Needham's sac Nephridia ("kidneys") Nidamental glands Osphradium Pericardial glands Funnel Foveola Funnel groove Funnel locking-apparatus Funnel organ Funnel retractor muscles Funnel valve Head and limbs Brachial crown Arms Hectocotylus Tentacles Carpus Dactylus Manus Suckers and hooks Buccal region Aptychus Beak Odontophore Radula Occipital region Occipital crest Occipital folds (nuchal folds) Occipital membrane Olfactory organ Nuchal organ Other parts Eyes Cornea Eye pore Eyelid sinus Secondary eyelid Statocysts General Chromatophores Photophores Nervous system Squid giant axon Squid giant synapse Developmental stages: Spawn → Paralarva (Doratopsis stage) → Juvenile → Subadult → Adult • Protoconch (embryonic shell)

v t e Vision in animals Vision Birds Cats Dinosaurs Dogs Fish Horses Toads Eyes Arthropod eye Eye shine Simple eye in invertebrates Mammalian eye Human eye Mollusc eye Cephalopod eye Gastropod eye Holochroal eye Parietal eye Schizochroal eye Evolution Evolution of the eye Evolution of color vision Evolution of color vision in primates Coloration Animal coloration Aposematism Camouflage Chromatophore Counter-illumination Countershading Crypsis Deimatic behaviour Eyespot (mimicry) Mimicry Structural coloration Underwater camouflage Related topics Animal senses Blind animals Eyespot apparatus Feature detection Infrared sensing in snakes Monocular deprivation Ommatidium Underwater vision Visual perception