Since 1939, scientists have thought the "barreleye" fish Macropinna microstoma had "tunnel vision" due to eyes that were fixed in place. Now though, Monterey Bay Aquarium researchers show that the fish actually has a transparent head and the eyes rotate around inside of it. From the Monterey Bay Aquarium Research Institute:
"Researchers solve mystery of deep-sea fish with tubular eyes and transparent head" (Thanks, Justin Ried!)
(Bruce) Robison and (Kim) Reisenbichler used video from MBARI's remotely operated vehicles (ROVs) to study barreleyes in the deep waters just offshore of Central California. At depths of 600 to 800 meters (2,000 to 2,600 feet) below the surface, the ROV cameras typically showed these fish hanging motionless in the water, their eyes glowing a vivid green in the ROV's bright lights. The ROV video also revealed a previously undescribed feature of these fish--its eyes are surrounded by a transparent, fluid-filled shield that covers the top of the fish's head.
Most existing descriptions and illustrations of this fish do not show its fluid-filled shield, probably because this fragile structure was destroyed when the fish were brought up from the deep in nets. However, Robison and Reisenbichler were extremely fortunate--they were able to bring a net-caught barreleye to the surface alive, where it survived for several hours in a ship-board aquarium. Within this controlled environment, the researchers were able to confirm what they had seen in the ROV video--the fish rotated its tubular eyes as it turned its body from a horizontal to a vertical position.