Tag Archives: sight

Gold-infused contact lenses that treat red-green color blindness could hit the market soon

New research is aiming to bring color back into the lives of the color-blind.

Image credits n4i Photo / Flickr.

Color blindness can manifest itself in several ways, from people seeing certain colors in muted shades to not perceiving some at all. Needless to say, this is not the most enjoyable way to live your life and can cause real issues with color-cues, such as difficulties navigating a traffic light. Some of our fixes so far include tinted glasses or dyed contact lenses, but they all have their own shortcomings. The glasses can’t be used to also correct vision (so some people need to pick one or the other condition to fix), and the lenses can be unstable, potentially harmful if not used properly.

A new paper, however, reports on a new approach that can help address this issue: infusing contact lenses with gold particles.

Blingvision

Color blindness is a genetic disorder so, for now, our best approach to the issue so far is to treat its symptoms. The main issue with contact lenses employed for this purpose is that, although they are effective in improving red-green color perception, clinical trials have shown that they can leech the pigments they’re dyed with, potentially harming users’ eyes.

The current paper describes how the authors used gold nanocomposite materials to produce lenses with the same effect, but no dye. This process has been used for centuries already to produce ‘cranberry’ glass, they explain, and comes down to how the gold scatters light going through the glass.

In order to produce them, the team put together an even mix of gold nanoparticles and a hydrogel polymer. The end result was a rose-tinted gel that filters light within the 520-580 nm range, which corresponds to the colors red and green. Several types of nanoparticles were tested, and those who were around 40 nm in diameter were the most effective. During lab testing, lenses built with nanoparticles of this size did not clump, nor did they over-filter the color.

The lenses have the same water-retention properties like those of commercial lenses, and were non-toxic to cell cultures in the lab.

After comparing their lenses’ efficiency to those of two commercially-available pairs of tinted glasses and the pink-dyed contact lenses. The gold-infused lenses blocked a narrower band of the visible spectrum, and a similar amount to that of the dyed contact lenses. This suggests that the gold nanocomposite lenses would be effective for people with red-green colorblindness, but without the health concerns.

The lenses will now undergo clinical trials to assess their efficiency, safety, comfort, and practicality with human patients in real-life situations. If they pass, we could see them available commercially.

The paper “Gold Nanocomposite Contact Lenses for Color Blindness Management” has been published in the journal ACS Nano.

Fossil Friday: this ancient bottom feeder could have ‘invented’ modern sight

A new paper examines how life first developed advanced eyes and sight, and how this led to an “evolutionary arms race” around 500 million years ago. The findings rely on radiodont fossils, a group of arthropods that were abundant in the ocean at the time.

Artist’s reconstruction of ‘Anomalocaris’ briggsi.

The radiodont order, meaning “radiating teeth”, is comprised of many species with a similar body layout — a head and a pair of segmented limbs that would capture prey. They had circular mouths with sharp, serrated teeth, and were roughly squid-shaped. They likely inhabited the deeper layers of the ocean, at around 1000 meters in depth. Due to the low light levels there, they evolved large, sophisticated eyes in order to catch prey. But this ‘sensor’ upgrade would send ripples throughout life on the planet, the authors explain, making vision a driving force in evolution as it pitted predator against prey.

See food, eat food

“Our study provides critical new information about the evolution of the earliest marine animal ecosystems,” said Professor John Paterson from the University of New England’s Palaeoscience Research Centre, lead author on the study.

“In particular, it supports the idea that vision played a crucial role during the Cambrian Explosion, a pivotal phase in history when most major animal groups first appeared during a rapid burst of evolution over half a billion years ago.”

The development of complex eyes allowed animals to perceive their surroundings better than ever before, which also helped predators spot prey more easily. But sight can also warn the hunted of the hunter, so it became a very powerful driver of evolution — after all, the one with poorer sight might not make it through the day. It has retained its importance up to today when virtually every ecosystem and ecological interaction on the planet is shaped by sight.

Acute zone–type eye of ‘A.’ briggsi. Image credits John R. Paterson, Gregory D. Edgecombe, and Diego C. García-Bellido, (2020), Science Advances.

The fossils used in this study were first unearthed around a century ago at Emu Bay Shale on South Australia’s Kangaroo Island and were comprised of isolated body parts. However, initial attempts to reconstruct the animals based on their fossils were quite unsuccessful and resulted in several “Frankenstein’s monsters”, the authors note. Over the decades, as more radiodont material was discovered, including whole bodies, we’ve gained a better understanding of these animals, their body structure, diversity, even possible lifestyles. Still, the specimens from Emu Bay Shale had some unique properties.

“The Emu Bay Shale is the only place in the world that preserves eyes with lenses of Cambrian radiodonts. The more than thirty specimens of eyes we now have, have shed new light on the ecology, behavior, and evolution of these, the largest animals alive half-a-billion years ago,” says Associate Professor Diego García-Bellido from the University of Adelaide and South Australian Museum, a co-author of the paper.

The team worked with these fossils before. They published two papers describing the fossilized eyes recovered from the site. The first one looked at isolated eye specimens of up to one centimeter in diameter, which remain unassigned to a species up to now. The second paper analyzed the eyestalks of Anomalocaris, a top predator in its day that grew up to one meter in length. The current paper, according to the authors, identifies that first, unknown species: ‘Anomalocaris’ briggsi, a new genus that “is yet to be formally named,” Prof. Paterson said.

Acute zone–type eye of ‘A.’ briggsi. Image credits John R. Paterson, Gregory D. Edgecombe, and Diego C. García-Bellido, (2020), Science Advances.

“We discovered much larger specimens of these eyes of up to four centimetres in diameter that possess a distinctive ‘acute zone’, which is a region of enlarged lenses in the centre of the eye’s surface that enhances light capture and resolution.”

The large lenses of these animals suggest that they could work in the dim light of the deep sea, and were likely very similar to those of modern amphipod crustaceans (a type of prawn-like creature). Anomalocaris briggsi primarily hunted plankton by filtration through its appendages; its eyes helped it spot its meals from the bottom of the ocean.

The body structure of these fossil species also showcases how different feeding strategies dictated differences in sight.

“The predator has the eyes attached to the head on stalks but the filter feeder has them at the surface of the head. The more we learn about these animals the more diverse their body plan and ecology is turning out to be,” says Dr Greg Edgecombe, a researcher at The Natural History Museum, London and co-author of the study.

“The new samples also show how the eyes changed as the animal grew. The lenses formed at the margin of the eyes, growing bigger and increasing in numbers in large specimens — just as in many living arthropods. The way compound eyes grow has been consistent for more than 500 million years.”

The paper “Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology” has been published in the journal Science Advances.

Researchers coax neurons into regenerating and restore vision in mice

Stanford University researchers have developed a method that allows them to regrow and form connections between neurons involved in vision. The method has been only tested on mice but the results suggest that mammalian brain cells can be restored after being damaged — meaning maladies including glaucoma, Alzheimer’s disease, and spinal cord injuries might be more repairable than has long been believed.

Neurons are the building blocks of our nervous system.
Image via youtube

It has long been believed that mammalian brain cells can’t regrow, but the new study shows that it’s possible. The team reports that they’ve managed to regenerate the axons of retinal ganglion cells, and although fewer than 5 percent of cells responded to the method, it was enough to make a difference in the mice’s vision.

“The brain is very good at coping with deprived inputs,” says Andrew Huberman, the Stanford neurobiologist who led the work. “The study also supports the idea that we may not need to regenerate every neuron in a system to get meaningful recovery.”

“I think it’s a significant step forward toward getting to the point where we really can regenerate optic nerves,” says Johns Hopkins professor of ophthalmology Don Zack, who was not involved in the research. “[It is] one more indication that it may be possible to bring that ability back in humans.”

The study shows that a regenerating axon can grow in the right direction, forming the connections needed to restore function.

“They can essentially remember their developmental history and find their way home,” Huberman says. “This has been the next major milestone in the field of neural regeneration.”

Once central nervous system cells reach maturity, they flip a genetic switch and never grow again. The team used genetic manipulation to flip this switch back on, activating the so-called “mammalian target of rapamycin” (mTOR) signaling pathway, which helps stimulate growth. At the same time, they exercised the damaged eye by showing mice a display of moving, high-contrast stripes.

“When we combined those two [methods]—molecular chicanery with electrical activity—we saw this incredible synergistic effect,” Huberman says. “The neurons grew enormous distances—500 times longer and faster than they would ordinarily.”

They observed that by covering the mice’s good eyes so they looked at the stripes only with their damaged eyes, the neurons regenerated faster. The team used a virus to deliver the altered genes to their mice, but study co-author Zhigang He believes there may be simpler ways to achieve this, such as pills, for human treatment. He, who developed the mTOR procedure, isn’t sure how the findings will impact human patients. He notes that a dual procedure, similar to that they used for the rats, hasn’t yet been developed for humans. He also pointed out that our retinal cells would have to grow a lot more than a mouse’s to rewire vision.

“The human optic nerve has to regenerate not on the scale of millimeters but on the scale of centimeters,” he explains.

Further research is needed to figure out the best use of this method for patients.

“Before, there was nothing to do” about damage to retinal nerves or other brain cells, says He, whose lab studies both retinal and spinal cord damage. “Now, we need to think about what type of patient might be most likely to benefit from the treatment.”

Huberman hopes that his method will be usable within a few years to help patients with early-stage glaucoma avoid the degeneration that leads to blindness.

“There are going to be many, many cases in which glaucoma could be potentially treated by enhancing the neural activity of retinal ganglion cells,” he says.

The findings also suggest that other brain cells could be determined to self-repair, Huberman says. Potential applications include restoring some movement after spinal cord damage, fighting memory-related diseases such as Alzheimer’s and even helping patients manage the symptoms of autism.

The full paper, titled “Neural activity promotes long-distance, target-specific regeneration of adult retinal axons” has been published in the journal Nature Neuroscience.

How the eye works

 

Image via flickr. 

Doing some light reading

Touch interprets changes of pressure, texture and heat in the objects we come in contact with. Hearing picks up on pressure waves, and taste and smell read chemical markers. Sight is the only sense that allows us to make heads and tails of some of the electromagnetic waves that zip all around us — in other words, seeing requires light.

Apart from fire (and other incandescent materials), bioluminiscent sources and man-made objects (such as the screen you’re reading this on) our environment generally doesn’t emit light for our eyes to pick up on. Instead, objects become visible when part of the light from other sources reflects off of them.

Let’s take an apple tree as an example. Light travels in a (relatively) straight line from the sun to the tree, where different wavelengths are absorbed by the leaves, bark and apples themselves. What isn’t absorbed bounces back and is met with the first layer of our eyes, the thin surface of liquid tears that protects and lubricates the organ. Under it lies the cornea, a thin sheet of innervated transparent cells.

Behind them, there’s a body of liquid named the aqueous humor. This clear fluid keeps a constant pressure applied to the cornea so it doesn’t wrinkle and maintains its shape. This is a pretty important role, as that layer provides two-thirds of the eye’s optical power.

Anatomy of the eye.
Image via flikr

The light is then directed through the pupil. No, there’s no schoolkids in your eye; the pupil is the central, circular opening of the iris, the pretty-colored part of our eyes. The iris contracts or relaxes to allow an optimal amount of light to enter deeper into our eyes. Without it working to regulate exposure our eyes would be burned when it got bright and would struggle to see anything when it got dark.

The final part of our eye’s focusing mechanism is called the crystalline lens. It only has half the focusing power of the cornea but its most important function is that it can change how it does this. The crystalline is attached to a ring of fibrous tissue on its equator, that pull on the lens to change its shape (a process known as accommodation), allowing the eye to focus on objects at various distances.

Fun fact: You can actually observe how the lens changes shape. Looking at your monitor, hold your up hands some 5-10 centimeters (2-4 inches) in front of your eyes and look at them till the count of ten. Then put them down; those blurry images during the first few moments and the weird feeling you get in your eyes are the crystalline stretching to adapt to the different focal vision.
Science at its finest.

After going through the lens, light passes through a second (but more jello-like) body of fluid and falls on an area known as the retina. The retina lines the back of the eye and is the area that actually processes the light. There are a lot of different parts of the retina working together to keep our sight crispy clear, but three of them are important in understanding how we see.

  • First, the macula. This is the “bull’s eye” of the retina. At the center of the macula there’s a slight dip named the fovea centralis (fovea is latin for pit). As it lies at the focal point of the eye, the fovea is jam-packed with light sensitive nerve endings called photoreceptors.
  • Photoreceptors. These differentiate in two categories: rods and cones. They’re structurally and functionally different, but both serve to encode light as electro-chemical signals.
  • Retinal pigment epithelium. The REP is a layer of dark tissue whose cells absorb excess light to improve the accuracy of our photoreceptors’ readings. It also delivers nutrients to and clears waste from the retina’s cells.

So far you’ve learned about the internal structure of your eyes, how they capture electromagnetic light, focus it and translate it into electro-chemical signals. They’re wonderfully complex systems, and you have two of them. Enjoy!

There’s still something I have to tell you about seeing, however. Don’t be alarmed but….

The images are all in your head

While eyes focus and encode light into the electrical signals our nervous system uses to communicate, they don’t see per se. Information is carried by the optical nerves to the back of the brain for processing and interpretation. This all takes place in an area of our brain known as the visual cortex.

Brain shown from the side, facing left. Above: view from outside, below: cut through the middle. Orange = Brodmann area 17 (primary visual cortex)
Image via wikipedia

Because they’re wedged in your skull a short distance apart from each other, each of your eyes feeds a slightly different picture to your brain. These little discrepancies are deliberate; by comparing the two, the brain can tell how far an object is. This is the mechanism that ‘magic eye’ or autostereogram pictures attempt to trick, causing 2D images to appear three dimensional.  Other clues like shadows, textures and prior knowledge also help us to judge depth and distance.

[YOU SHOULD  ALSO READ] The peculiar case of a woman who could only see in 2-D for 48 years, and the amazing procedure that gave her stereo-vision

The neurons work together to reconstruct the image based on the raw information the eyes feed them. Many of these cells respond specifically to edges orientated in a certain direction. From here, the brain builds up the shape of an object. Information about color and shading are also used as further clues to compare what we’re seeing with the data stored in our memory to understand what we’re looking at. Objects are recognized mostly by their edges, and faces by their surface features.

Brain damage can lead to conditions that impair object recognition (an inability to recognize the objects one is seeing) such as agnosia.  A man suffering from agnosia was asked to look at a rose and described it as ‘about six inches in length, a convoluted red form with a linear green attachment’. He described a glove as ‘a continuous surface infolded on itself, it appears to have five outpouchings’. His brain had lost its ability to either name the objects he was seeing or recognize what they were used for, even though he knew what a rose or a glove was. Occasionally, agnosia is limited to failure to recognize faces or an inability to comprehend spoken words despite intact hearing, speech production and reading ability.

The brain also handles recognition of movement in images. Akinetopsia, a movement-recognition impairing condition is caused by lesions in the posterior side of the visual cortex. People suffering from it stop seeing objects as moving, even though their sight is otherwise normal. One woman, who suffered such damage following a stroke, described that when she poured a cup of tea the liquid appeared frozen in mid-air, like ice. When walking down the street, she saw cars and trams change position, but not actually move.

photo: vimeo.com

Cyber synesthesia: computer turns image into sound, allowing the blind to ‘see’

photo: vimeo.com

photo: vimeo.com

After growing up to adulthood blinded from birth, a man now has taken a peculiar hobby: photography. Were it not for the efforts of a group of researchers who have devised a system that converts images into sequences of sound, this new found pastime had been impossible. Hobbies or not, the technology is particular impressive and judging from the stream of data reported thus far, it could prove to be a marvelous system for everyday use, helping the blind navigate their surroundings, recognize people and even appreciate visual arts — all through sound.

In all began in 1992 when a Dutch engineer called  Peter Meijer invented vOICe – an algorithm that converted simple grayscale, low-resolution images into sounds that would break into an unique, discernible pattern by the trained ear. As the algorithm scans from left to right, each pixel or group of pixels has a corresponding frequency (higher positions in the image  –> higher acoustic frequencies). A simple image, for instance, only showing  a diagonal line stretching upward from left to right becomes a series of ascending musical notes, while a more complicate image, say a man leaning on a chair, turns into a veritable screeching spectacle.

Amir Amedi and his colleagues at the Hebrew University of Jerusalem took things further and made vOICe portable, while also studying the participants’ brain activity for clues. They recruited people that had been blind all their lives from birth, but after just 70 hours of training and obviously despite any visual cues,   the individuals went from “hearing” simple dots and lines to “seeing” whole images such as faces and street corners composed of 4500 pixels. Mario on Nintendo only has 192 pixels and it still felt freaking realistic sometimes (was that just me as kid or what?).

Seeing with sound

Using head-mounted cameras that communicated with the vOICe technology, the blind participants could then navigate their surroundings and even recognize human silhouettes. To prove they could visually sense accurately, the  participants mimicked the silhouette’s stances.

Things turned really interesting when the researchers analyzed the brain activity data. The traditional sensory-organized brain model says the brain is organized in regions each devoted to certain senses. For instance, the visual cortex is used for sight processing; in the blind, where these areas aren’t used conventionally, these brain regions are re-purposed to boost some other sense, like hearing. Amedi and colleagues found, however,  that the area of the visual cortex responsible for recognizing body shapes in sighted people was signaling powerfully when the blind participants were  interpreting the human silhouettes. Neuroscientist Ella Striem-Amit of Harvard University, who co-authored the paper, thinks it’s time for a new model. “The brain, it turns out, is a task machine, not a sensory machine,” she says. “You get areas that process body shapes with whatever input you give them—the visual cortex doesn’t just process visual information.”

“The idea that the organization of blind people’s brains is a direct analog to the organization of sighted people’s brains is an extreme one—it has an elegance you rarely actually see in practice,” says Ione Fine, a neuroscientist at the University of Washington, Seattle, who was not involved in the study. “If this hypothesis is true, and this is strong evidence that it is, it means we have a deep insight into the brain.” In an alternative task-oriented brain model, parts of the brain responsible for similar tasks—such as speech, reading, and language—would be closely linked together.

The team also devised a vOICe version that can be run as a free iPhone app, called EyeMusic. The researchers demonstrated that using the app, blind participants could recognize drawn faces and distinguish colours. The video below showcases the app. The study was reported in the journal Current Biology.

source: scimag