First vertebrate eye to use mirror

Scientists have discovered a new fish in the deep waters between Samoa and New Zealand, which is the first vertebrate found with eyes that use mirrors, rather than a lens, to focus light.

According to a report in New Scientist, the unusual fish, known as 'Spookfish', actually has just two eyes, but each eye has two parts, one looking upwards and the other down.

The team found that the part looking down uses thousands of tiny reflective crystals acting like mirrors that are angled in slightly different directions to focus light onto the retina. This is completely different to a typical fish eye, which uses a single lens to bend light onto a focal point, similar to the way the human eye works. Other tubular-eyed fish do use optical techniques to look sideways and downwards but these mechanisms have no way to focus light into a clear image.

The spookfish is the only deep-sea fish with eyes that have been shown to produce a focused image when looking both up and down. "This is the first demonstration that vertebrates are not as optically boring as we thought," said Douglas. According to Mike Land from the University of Sussex, UK, the eye is "intriguing" and could be unique to the spookfish. "I doubt we'll see this in other vertebrates. Had it been,we would have surely discovered it by now," he said.