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Extraocular Vision: The ability to see without eyes

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Although vision is one of our five senses, you might be surprised to learn that some animals don't require it at all! We can think of several animals that, instead of seeing with their eyes, can use a variety of other senses to comprehend their surroundings, travel, and so on. Extraocular vision is the ability to see without using your eyes. It has been defined by previous researchers as the ability to resolve scenes without the use of discrete eyes. Fascinating research: Extraocular Vision Researchers believe that the photoreceptor cells found on the bodies of sea urchins and brittle stars aid extraocular vision. Brittle stars were placed in a circular arena in the laboratory by scientists from the University of Oxford, who published their findings in Current Biology. The brittle stars moved toward white walls with a black bar, which suggested a daytime hideaway. Even with grey walls, the eye was drawn to the black stripe, which was centered on a white stripe. According to the researchers, a brittle star sees through light-sensing cells that cover its entire body. The brittle star receives visual stimuli from these light-sensing cells, allowing it to recognise coarse structures like rocks, according to the research. It has this unusual ability thanks to light-sensing cells called photoreceptors that cover its body and pigment cells called chromatophores that move during the day to allow the animal to change colour from a deep reddish-brown during the day to a stripy beige at night. "It's a thrilling discovery." "We're very happy to be able to fill in some of the gaps that remained and describe this new mechanism," Lauren Sumner-Rooney, a research fellow at Oxford University Museum of Natural History who studies unusual visual systems, said in a statement released by the university. "It had been suggested 30 years ago that changing colour might hold the key to light-sensitivity in Ophiocoma, so we're very happy to be able to fill in some of the gaps that remained and describe this new mechanism," ANIMALS THAT POSSESS EXTRAOCULAR VISION Several animals can see without eyes, i.e. they possess extraocular vision. Let's have a look at them: TEXAS SALAMANDER For several years, the Texas Blind Salamander has been living in underground waters. These creatures lack eyes and have evolved to the point where they can function without them. This animal travels and hunts for food using water pressure waves rather than sight. SEA URCHINS Sea urchins react to light in a variety of ways, including changing colour, twitching their spines, and moving toward or away from the source of light. Scientists have known this for decades, but they've never been able to figure out how urchins detect light because no known species of these creatures have eyes. The researchers discovered that the net of nerves that encircled an urchin's body contained some diffused light-sensitive tissue. Recent studies and research have revealed that sea urchins have a far more organised visual system than previously thought. HYDRAS Hydras have thin tubular bodies crowned with slender tentacles and are considered jellyfish relatives. They usually cling to weeds, stinging and eating even tinier aquatic invertebrates like water fleas as they swim by (daphnia). Even though they don't have eyes, hydras, like sea urchins, respond to light. SWALLOWTAIL BUTTERFLIES While they lack eyes, Japanese yellow swallowtail butterflies can see with their back ends. They have two photoreceptors, which are light-sensitive neurons, on their abdomens, right next to their genitals! MEXICAN TETRA The Mexican Tetra is a cave-dwelling blind fish that has adapted to its dark surroundings. The fish's lack of eyes is one of the most obvious signs of this adaptation. The water pressure helps these non-sighted swimmers navigate. What's more surprising is that, even though fishes have survived for generations without eyes, they can sometimes produce sighted offspring. Humans have extraocular muscles With the help of the extraocular muscles, we constantly direct our gaze to the object of interest and thus use foveal fixation to achieve the best possible visual acuity. The muscles around the eye area are rather different from other skeletal muscles, being, for example, simultaneously the fastest muscles in the body and impossible to exhaust. The most exciting property of the extraocular muscles is their unique response to disease, as they often remain unaffected in muscle conditions that lead to severe handicap and premature death. Understanding the coping mechanisms that allow the extraocular muscles to remain unaffected could lead to new treatments for severe diseases like muscle dystrophies in the future.

Although vision is one of our five senses, you might be surprised to learn that some animals don’t require it at all! We can think of several animals that, instead of seeing with their eyes, can use a variety of other senses to comprehend their surroundings, travel, and so on.

Extraocular vision is the ability to see without using your eyes. It has been defined by previous researchers as the ability to resolve scenes without the use of discrete eyes.

 

Fascinating research: Extraocular Vision

 

Researchers believe that the photoreceptor cells found on the bodies of sea urchins and brittle stars aid extraocular vision. Brittle stars were placed in a circular arena in the laboratory by scientists from the University of Oxford, who published their findings in Current Biology. The brittle stars moved toward white walls with a black bar, which suggested a daytime hideaway. Even with grey walls, the eye was drawn to the black stripe, which was centered on a white stripe.

 

According to the researchers, a brittle star sees through light-sensing cells that cover its entire body. The brittle star receives visual stimuli from these light-sensing cells, allowing it to recognise coarse structures like rocks, according to the research.

It has this unusual ability thanks to light-sensing cells called photoreceptors that cover its body and pigment cells called chromatophores that move during the day to allow the animal to change colour from a deep reddish-brown during the day to a stripy beige at night.

 

“It’s a thrilling discovery.” “We’re very happy to be able to fill in some of the gaps that remained and describe this new mechanism,” Lauren Sumner-Rooney, a research fellow at Oxford University Museum of Natural History who studies unusual visual systems, said in a statement released by the university. “It had been suggested 30 years ago that changing colour might hold the key to light-sensitivity in Ophiocoma, so we’re very happy to be able to fill in some of the gaps that remained and describe this new mechanism,”

 

ANIMALS THAT POSSESS EXTRAOCULAR VISION

 

Several animals can see without eyes, i.e. they possess extraocular vision. Let’s have a look at them:

 

TEXAS SALAMANDER

 

For several years, the Texas Blind Salamander has been living in underground waters. These creatures lack eyes and have evolved to the point where they can function without them. This animal travels and hunts for food using water pressure waves rather than sight.

 

SEA URCHINS

 

Sea urchins react to light in a variety of ways, including changing colour, twitching their spines, and moving toward or away from the source of light. Scientists have known this for decades, but they’ve never been able to figure out how urchins detect light because no known species of these creatures have eyes. The researchers discovered that the net of nerves that encircled an urchin’s body contained some diffused light-sensitive tissue. Recent studies and research have revealed that sea urchins have a far more organised visual system than previously thought.

 

HYDRAS

 

Hydras have thin tubular bodies crowned with slender tentacles and are considered jellyfish relatives. They usually cling to weeds, stinging and eating even tinier aquatic invertebrates like water fleas as they swim by (daphnia). Even though they don’t have eyes, hydras, like sea urchins, respond to light.

 

SWALLOWTAIL BUTTERFLIES

 

While they lack eyes, Japanese yellow swallowtail butterflies can see with their back ends. They have two photoreceptors, which are light-sensitive neurons, on their abdomens, right next to their genitals!

 

MEXICAN TETRA

 

The Mexican Tetra is a cave-dwelling blind fish that has adapted to its dark surroundings. The fish’s lack of eyes is one of the most obvious signs of this adaptation. The water pressure helps these non-sighted swimmers navigate. What’s more surprising is that, even though fishes have survived for generations without eyes, they can sometimes produce sighted offspring.

 

Humans have extraocular muscles

 

With the help of the extraocular muscles, we constantly direct our gaze to the object of interest and thus use foveal fixation to achieve the best possible visual acuity. The muscles around the eye area are rather different from other skeletal muscles, being, for example, simultaneously the fastest muscles in the body and impossible to exhaust. The most exciting property of the extraocular muscles is their unique response to disease, as they often remain unaffected in muscle conditions that lead to severe handicap and premature death. Understanding the coping mechanisms that allow the extraocular muscles to remain unaffected could lead to new treatments for severe diseases like muscle dystrophies in the future.

 


Also published on Medium.

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