Tag Archives: Seeing

Novel glasses can help the color-blind perceive more colors

New research from the UC Davis Eye Center and France’s INSERM Stem Cell and Brain Research Institute could provide glasses that help the color-blind perceive hues.

Image via Pixabay.

As of now, the glasses use “advanced spectral notch filters” to enhance the color-perceiving ability for patients with anomalous trichromacy, the most common type of red-green color vision deficiency (CVD). This effect seemed to persist even after participants took the glasses off, the team adds.

Color-seeing glasses

“Extended usage of these glasses boosts chromatic response in those with anomalous trichromacy (red-green color vision deficiency),” said John Werner, distinguished professor of ophthalmology and a leader in vision science at UC Davis Health, first author of the study.

“We found that sustained use over two weeks not only led to increased chromatic contrast response, but, importantly, these improvements persisted when tested without the filters, thereby demonstrating an adaptive visual response.”

According to the team, 7% of men and 0.5% of women worldwide suffer from CVD — a total of 13 million in the US and 350 million globally. UC Davis, they estimate, has around 1,700 students with red-green CVD.

People with CVD see colors as more muted and washed-out. They have a hard time differentiating between some colors and can perceive a much smaller color palate than an individual with normal color vision.

File:Eight Ishihara charts for testing colour blindness, Europe Wellcome L0059163.jpg
Eight Ishihara charts for testing color blindness, still in use today.
Image credits Medical Photographic Library

The glasses devised by the team use spectral notch filters, which attenuate part of the visible light that hits them. These “EnChroma glasses” should help CVD patients better distinguish colors and make them seem more vibrant and distinct by increasing the separation between different-colored wavelengths of light.

They were given to participants to wear over two weeks. They were asked to keep a diary and were re-tested on days 2, 4, and 11 without wearing the glasses. Another group of students received normal (placebo) glasses.

Individuals with red-green CVD showed a higher ability to distinguish these colors, the team found. This effect persists for some time after wearing the glasses, as revealed by participants’ performance during the re-tests, although it is yet unclear as to how long the effect lasts.

Alex Zbylut, one of the color blind participants in the study, first received the placebo glasses and was then given the experimental ones to try out. He explains that when he goes outside wearing these glasses, “all the colors are extremely vibrant and saturated, and I can look at trees and clearly tell that each tree has a slightly different shade of green compared to the rest. I had no idea how colorful the world is and feel these glasses can help color blind people better navigate color and appreciate the world.”

Werner says this effect can’t be achieved with broad-band filters sold as aids to the color blind. The findings might point to changes in brain networks or processing patterns causing the observed effect — and which may be used as an avenue for treatment in the future.

The paper “Adaptive Changes in Color Vision from Long-Term Filter Usage in Anomalous but Not Normal Trichromacy,” has been published in the journal Current Biology.

Scientists find a woman that can see 99 million more colors than you or me

Neuroscientists in the UK have recently announced that their 25 year long search for a tetracromath — a person with an extra type of cone cell in his or her retina — has finally come to a successful end. They estimate that the woman can see a staggering 99 million more colors than other humans, and they believe there are many more people like her waiting to be discovered.

Image via pixabay

Our eyes‘ retina house cone cells that can distinguish color variation in incoming light. Humans usually have three types of cone cells, each able to detect the presence of a single color — green, red, or blue — and are thus known as “trichromats.” Most color blind people and most other mammals only have two different types of cone cells, and are “bichromats.” As each cell can distinguish between 100 or so shades of the same color, each extra type of cone cell increases the number of colors we can see exponentially. So where a color blind person can see around 10,000 shades, a healthy human can see around 1 million different colors.

But what if human beings had not three, but four types of cone cells in their retinas? That would allow a person to see 100 million colors — colors most of us have never even dreamed of, colors we have no way of even imagining. The existence of such people, or “tetrachromats,” was first proposed in 1948 by Henri Lucien de Vries, a Dutch scientist researching with color blind patients. He found that while his male subjects had two types of normal cone cells and one mutant type that was less sensitive and didn’t pick up on its corresponding color (either green or red,) the female subjects had three normal cone cell types and one mutant type. Even if this extra type of cell didn’t actually do anything, it suggested that humans can have more than three types of cells.

Interest in tetrachromats largely died out until the late ’80s, when Professor John Mollon from Cambridge University started looking for women who might have four functioning cone cell types. He estimated that, if color blind men could pass this fourth cell type to their daughters, around 12% of the female population should be tetrachomats. However, he never actually found a person with four different fully functional types of cone cells, a tetrachromat.

But now, 25 years after they’ve first started searching, UK scientists believe they’ve finally found such a woman. Known as cDa29, she was identified by Newscastle University neuroscientist Gabriele Jordan, a former coleague of Mollon, after she decided to use a different test than those the professor employed in his search.

She took 25 women who had a fourth type of cone cell, and put them in a dark room. Looking into a light device, three colored circles of light flashed before these women’s eyes. To you and me the circles would look the same, but Jordan believed that a true tetrachromat could tell them apart, as the fourth type of cone cells would allow her to pick up on the subtle differences.

One of the women tested, cDa29, was able to differentiate the three different colored circles on every single try.

“I was jumping up and down,” Jordan told Discover magazine.

But why did it take so long to find a tetracromat if there’s so many of them? One issue is that the team only carried out their search in the UK. But more importantly, Jordan says, is that most true tetrachromats simply don’t know they’re any different from the rest of us.

“We now know tetrachromacy exists,” she said. “But we don’t know what allows someone to become functionally tetrachromatic, when most four-coned women aren’t.”

Jay Neitz, a vision researcher at the University of Washington, who wasn’t involved in the study, thinks that tetrachromats simply haven’t had a chance to use their eyes to their full potential in our society.

“Most of the things that we see as coloured are manufactured by people who are trying to make colours that work for trichromats,” he said. “It could be that our whole world is tuned to the world of the trichromat.”

The research on cDa29 hasn’t been peer-reviewed or published as yet, and Jordan is continuing her research and search for more tetrachromats. Her results still need to be verified but if tetrachromats really do exist, it could teach us a lot about how vision works.

One thing we might never be able to understand, however, is exactly what the world looks like through cDa29’s eyes.

“This private perception is what everybody is curious about,” Jordan told Discover. “I would love to see that.”

Half the world will need glasses by 2050

Nearly half the world’s population, close to some 5 billion people, will develop myopia by 2050 according to a study recently published in the journal Ophthalmology. The paper also estimates that one-fifth of these people will have a significantly increased risk of becoming permanently blind from the condition if recent trends continue.

"Can you come a bit closer? I can't see you yet." Image via flikr @ Paul Stevenson.

“Can you come a bit closer? I can’t see you yet.”
Image via flikr @ Paul Stevenson.

The number of myopia cases is rapidly rising across the globe, making it one of the most common sight-impairment conditions of the modern world. This increase is attributed to “environmental factors (nurture), principally lifestyle changes resulting from a combination of decreased time outdoors and increased near work activities, among other factors,” according to a new study from Brien Holden Vision Institute, University of New South Wales Australia and Singapore Eye Research Institute.

Even worse, if the current trends continue, the paper warns that we’ll see a seven-fold increase in cases from 2000 to 2050. Myopia will also become one of the leading causes of permanent blindness by that date.

But why? Short-sightedness has always been around but never at the scale this study predicts.

It’s mostly due to the way we use our eyes today. For most purposes, our eyes are good at spotting far away objects, but they have been mostly relegated to short distance duty nowadays. Our daily activities involve a lot of “near work activities,” such as using a computer, scrolling on a smartphone or reading. Constantly keeping focus on a short distance leaves the crystalline lens in our eyes set on them, in a sense, and unable to effectively focus on objects farther away.

The authors point out that this has become a major public health issue, one that we’ll have to tackle — preferably sooner rather than later. They suggest that planning for comprehensive eye care services is needed to manage the rapid increase in high myopes (a five-fold increase from 2000), along with the development of treatments to control the progression of myopia and prevent people from becoming highly myopic.

“We also need to ensure our children receive a regular eye examination from an optometrist or ophthalmologist, preferably each year, so that preventative strategies can be employed if they are at risk,” said co-author Professor Kovin Naidoo, CEO of Brien Holden Vision Institute. “These strategies may include increased time outdoors and reduced time spent on near based activities including electronic devices that require constant focussing up close.

“Furthermore there are other options such as specially designed spectacle lenses and contact lenses or drug interventions but increased investment in research is needed to improve the efficacy and access of such interventions.”

Yea so….I’d say investing in the glasses industry will probably net you a nice return in a few years.

But there is an upside to this paper. Don’t want myopia? Drop your laptop and spend some time in the park. Put your smartphone in your pocket and look at the city as you walk to work or school. You might even end up having fun.

The full paper, titled “Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050” is available online in the journal Ophthalmology here.

 

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.

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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.