Scientists Find First Creature With Eyes That Use Both Refractive and Reflective Optics

Jan 27, 2009
Side view of the head of the Spookfish, showing the eye split into parts. The transparent head allows the fish to capture and process even more ambient light.

Florida Atlantic University researcher and member of the Center for Ocean Exploration and Deep-Sea Research at Harbor Branch Oceanographic Institute, Dr. Tamara Frank, was part of an international research team that discovered the first vertebrate with eyes that use mirrors rather than lenses to focus light. Results from this research have been published in the January issue of Current Biology.

The article, titled “A Novel Vertebrate Eye Using Both Refractive and Reflective Optics,” describes the unusual eyes of the spookfish, Dolichopteryx longipes. These eyes are tubular, which are similar in structure to the eyes of many other fish that swim in the ocean’s twilight zone where the background light field is very dim.

“What makes this animal so unusual is that each eye is divided into two parts, one pointing upwards and one pointing downwards, making it look like it has four eyes, and four-eyed fish don’t exist,” said Frank.

In the few other species of deep-sea fish that possess split eyes, the upper eye has a lens, like in the spookfish, for focusing light. However, at these depths, there is so little upwelling light that a lens would attenuate light too much in its efforts to focus the light for the lower eye. Therefore, in other fish, the lower eye doesn’t have a lens, resulting in a blurred image. The spookfish however, manages to focus light in the lower eye without using a lens. Light enters the lower portion of the eye and hits a mirror composed of stacks of crystals. The stacks sit roughly parallel to one another, but their angle changes over the surface of the mirror, giving it an overall concave shape. A computer simulation by research team member Dr. Julian Partridge, Bristol University, United Kingdom, showed that orientation of the plates within the mirror's curved surface is perfect for focusing reflected light onto the fish's retina. This is the first time that this type of focusing mechanism has ever been found in a vertebrate.

Many deep-sea or night active animals (including dogs and cats) use mirrors behind the retina to make their eyes more sensitive to light, hence why their eyes seem to glow when a light shines on them. It has been estimated that this reflecting layer, the tapetum, doubles the sensitivity of the eyes that possess them. With these animals, the mirror sits behind the eye and cannot focus light. In the spookfish, the mirror sits in front of the retina and serves to focus light, providing an image that’s much brighter than a lens could produce.

“While this species was first described 120 years ago, the few specimens that have been collected in the past were dead and quite mangled, so very little could be discerned about their visual systems,” said Frank.

The expedition, led by Dr. Hans-Joachim Wagner from Tübingen University in Germany on the German research vessel Sonne, utilized Frank’s “Tucker Trawl,” built by Harbor Branch’s engineering division. The opening/closing net has a special temperature-insulated collecting vessel at the end that can be closed at depth.

This feature enabled the scientists to secure the first-ever living specimen of this very rare fish from a depth of 700 meters over the Tonga Trench off Samoa. Pictures of the live animal immediately revealed that there was something unusual about the eye. Once back on land, the scientists examined the structure of the eye and discovered its unique properties.

Source: Florida Atlantic University

Explore further: Male monkey filmed caring for dying mate (w/ Video)

add to favorites email to friend print save as pdf

Related Stories

The science of anatomy is undergoing a revival

Apr 10, 2014

Only two decades ago, when I was starting my PhD studies at the University of California in Berkeley, there was talk about the death of anatomy as a research subject. That hasn't happened. Instead the science ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

gopher65
not rated yet Jan 28, 2009
Wasn't this exact same story put out on this site 20 days ago? Oh look, there is a link to it in the "related stories" section.

Physorg needs to pay more attention to their automated copy/paste process so that this sort of thing doesn't happen.
photojack
not rated yet Mar 04, 2009
Still an amazing story, even if repeated 20 days ago. Sort of does away with the "irreducible complexity" hogwash from the Creationist goons!

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.