The Jeweled Squid, Stigmatoteuthis arcturi (top left), is an interesting mesopelagic squid.
Among its peculiarities is that one eye is much larger than the other. The eyes may serve different functions, with the squid orienting its body to use its large eye to look upward for predators and prey silhouetted by whatever light may reach it from the surface. The other eye presumably detects bioluminescence below the animal.
The ventral surface of the deepwater squid Enoploteuthis chuni (bottom) is covered with photophores that produce bioluminescence for counterillumination. Another squid with differently sized eyes is the Cock- eyed Squid, Histoteuthis corona (top right).
This image is taken from Danté Fenolio's book Life in the Dark, published by Johns Hopkins University Press.