The vampire squid from hell, or Vampyroteuthis infernalis,1,2 is a small deep-sea cephalopod that has dark-red skin, winglike fins, purplish web, and eyes that can appear red or blue depending on lighting. It possesses the largest eyes of any animal in the world in proportion to its size. At an average length of about 6 to 9 in, the squid has globular eyeballs an inch across, or the size of a large dog’s. Inside the eye is a finely tuned spherical lens with a refractive index gradient from the center to the edge. This is achieved by varying concentration of crystallin proteins, which increases toward the center of the lens. These crystallin proteins appeared early in the evolution of cephalopods and are thought to produce excellent visual acuity in these animals. The vampire squid also has light-emitting organs called photophores at the base of its fins and the tips of the arms, which are useful for living in deep-sea darkness 3000 ft below the surface. The animal can even produce a glowing cloud around itself by releasing bioluminescent particles to disorient potential predators.
Rozenbaum I, Ritch R. Eye on the Web. Arch Ophthalmol. 2007;125(7):915. doi:10.1001/archopht.125.7.915