Posts tagged vision
Articles and news from the latest research reports.
Altering eye cells may one day restore vision
Doctors may one day treat some forms of blindness by altering the genetic program of the light-sensing cells of the eye, according to scientists at Washington University School of Medicine in St. Louis.
Working in mice with retinitis pigmentosa, a disease that causes gradual blindness, the researchers reprogrammed the cells in the eye that enable night vision. The change made the cells more similar to other cells that provide sight during daylight hours and prevented degeneration of the retina, the light-sensing structure in the back of the eye. The scientists now are conducting additional tests to confirm that the mice can still see.
“We think it may be significantly easier to preserve vision by modifying existing cells in the eye than it would be to introduce new stem cells,” says senior author Joseph Corbo, MD, PhD, assistant professor of pathology and immunology. “A diseased retina is not a hospitable environment for transplanting stem cells.”
The study is available in the early online edition of Proceedings of the National Academy of Sciences.
Mutations in more than 200 genes have been linked to various forms of blindness. Efforts are underway to develop gene therapies for some of these conditions.
Rather than seek treatments tailored to individual mutations, Corbo hopes to develop therapies that can alleviate many forms of visual impairment. To make that possible, he studies the genetic factors that allow cells in the developing eye to take on the specialized roles necessary for vision.
Why Do Age-Related Macular Degeneration Patients Have Trouble Recognizing Faces?
Abnormalities of eye movement and fixation may contribute to difficulty in perceiving and recognizing faces among older adults with age-related macular degeneration (AMD), suggests a study “Abnormal Fixation in Individuals with AMD when Viewing an Image of a Face” appearing in the January issue of Optometry and Vision Science, official journal of the American Academy of Optometry. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.
Unlike people with normal vision focus, those with AMD don’t focus on “internal features” (the eyes, nose and mouth) when looking at the image of a face, according to the study by William Seiple, PhD, and colleagues of Lighthouse International, New York.
When Viewing Famous Face, AMD Patients Focus on External Features
The researchers used a sophisticated technique called optical coherence tomography/scanning laser ophthalmoscopy (OCT-SLO) to examine the interior of the eye in nine patients with AMD. Age-related macular degeneration is the leading cause of vision loss in older adults. It causes gradual destruction of the macula, leading to blurring and loss of central vision.
Previous studies have suggested that people with AMD have difficulty perceiving faces. To evaluate the possible role of abnormal eye movements, Dr Seiple and colleagues used the OCT-SLO equipment to make microscopic movies of the interior of the eye (fundus, including the retina and macula) as the patients viewed one of the world’s most famous faces: the Mona Lisa.
This technique allowed the researchers to record eye movements and where the patients looked (fixations) while looking at the face. They compared the findings in AMD patients to a control group of subjects with normal vision.
The results showed significant differences in eye movement patterns and fixations between groups. The AMD patients had fewer fixations on the internal features of the Mona Lisa’s face—eyes, nose, and mouth. For controls, an average of 87 percent of fixations were on internal features, compared to only 13 percent on external features. In contrast, for AMD patients, 62 percent of fixations were on internal features while 38 percent were on external features.
The normal controls also tended to make fewer and shorter eye movements (called saccades) than AMD patients. The differences between groups did not appear to be related to the blurring of vision associated with AMD.
Some older adults with AMD report difficulties perceiving faces. While the problem in “processing faces” is certainly related to the overall sensory visual loss, the new evidence suggests that specific patterns of eye movement abnormalities may also play a role.
Dr Seiple and colleagues note that “abnormal scanning patterns when viewing faces” have also been found in other conditions associated with difficulties in face perception, including autism, social phobias, and schizophrenia. The authors discuss the possible mechanisms of the abnormal scanning patterns in AMD, involving the complex interplay between the eyes and brain in governing eye movement and interpreting visual information.
A previous study suggested that drawing attention to specific characteristics—such as the internal facial features—may increase fixations on internal features and improve face perception. Dr Seiple and coauthors conclude, “That report gives hope that eye movement control training and training of allocation of attention could improve face perception and eye scanning behavior in individuals with AMD.”
Faster help for stroke victims
Scientists have developed a quick, easy and cheap vision test to find out which part – and how much – of the brain of a stroke victim has been damaged, potentially enabling them to save more lives.
The test requires patients to look into a device for about ten minutes, enabling it to be used in the early stages of a stroke – even if the patient cannot move their limbs or speak.
This can help doctors diagnose and treat the stroke quickly and accurately, which is vital, as early treatment can greatly improve a person’s chances of survival and recovery, say Dr Corinne Carle and Professor Ted Maddess from The Vision Centre and The Australian National University.
According to the World Health Organisation, stroke is currently the world’s sixth commonest cause of death, accounting for 4.9% of all fatalities. In Australia it kills about 9000 people a year and hospitalises 35,000.
“Our new test automatically tracks the response of the patient’s eye pupils to different colours, and can show doctors whether the injury is located in the evolutionarily ‘new brain’ or the ‘old brain’,” Dr Carle says.
“The distinction is important because the ‘old brain’, or midbrain, controls things like the heart rate and blood pressure of the body. So if you find that the midbrain has been damaged, you’ll need to treat the patient much more aggressively, because there’s a higher risk of death.”
On the other hand, an injury in the ‘new brain’ – the cortex – may cause permanent blindness in a part of the person’s visual field, or difficulty in their thoughts, speech and movement, but has a lower risk of death, she says.
Using the TrueField Analyzer, a device developed by Prof. Maddess’ Vision Centre team and the Australian company Seeing Machines, the researchers tested how the pupils respond to images on LCD screens. A mixture of red, green and yellow coloured stimuli were provided to each eye, at 24 locations in the person’s visual field.
Two video cameras using infrared lighting recorded the instant response of the pupils, which was then analysed by a computer.
The colours red, green and yellow were chosen because they are processed by different parts of the brain, Dr Carle explains. In mammals, the cortex, or ‘new brain’, is the most recently evolved area, and allows humans to differentiate between red and green.
The ‘ancient’ midbrain, on the other hand, is red-green colourblind, but can detect the colour yellow.
“If the pupils don’t react when red changes to green, we know that the damage is in the cortex. The same concept applies to the yellow stimulus,” says Dr Carle. “The test has been successful in checking the vision of people with glaucoma or type-1 diabetes, and we have now tweaked the stimuli for stroke patients as well.”
Prof. Ted Maddess says that the test will complement various types of brain scans.
“A CT scan tells you where the bleed is, but it doesn’t show you everything,” he says. “For instance, the blood could have cleared up in a particular part of the brain during the scan, or where swelling has reduced the function of a nearby part that looks fine on the scan. It may also miss injuries that are too small, or those that occur in the midbrain, where it doesn’t scan well.”
This is where the test can be useful, Prof. Maddess says. As every single vision cell is wired into a different part of the brain, by testing a particular area in the visual field, doctors can check if the corresponding part of the brain is functioning or not.
The test can be used to monitor stroke patients’ recovery, Prof. Maddess says: “Currently, apart from brain scans, there is no cheap, routine test that can quantify the amount of improvement that results from a treatment. Stroke patients have a very high risk of recurrence, so it’s important that doctors can accurately assess their recovery.”
“The TrueField Analyzer is small, affordable and the test only takes ten minutes,” he says. Working together with neurologists, the research team will start clinical tests with stroke patients in February this year.
The team’s study “The pupillary response to color and luminance variant multifocal stimuli” by Corinne F. Carle, Andrew C. James and Ted Maddess is published in the latest issue of Investigative Ophthalmology & Visual Science (IOVS).
(Source: scinews.com.au)
Why Do We Blink So Frequently?
We all blink. A lot. The average person blinks some 15-20 times per minute—so frequently that our eyes are closed for roughly 10% of our waking hours overall.
Although some of this blinking has a clear purpose—mostly to lubricate the eyeballs, and occasionally protect them from dust or other debris—scientists say that we blink far more often than necessary for these functions alone. Thus, blinking is physiological riddle. Why do we do it so darn often? In a paper published in the Proceedings of the National Academy of Sciences, a group of scientists from Japan offers up a surprising new answer—that briefly closing our eyes might actually help us to gather our thoughts and focus attention on the world around us.
The researchers came to the hypothesis after noting an interesting fact revealed by previous research on blinking: that the exact moments when we blink aren’t actually random. Although seemingly spontaneous, studies have revealed that people tend to blink at predictable moments. For someone reading, blinking often occurs after each sentence is finished, while for a person listening to a speech, it frequently comes when the speaker pauses between statements. A group of people all watching the same video tend to blink around the same time, too, when action briefly lags.
As a result, the researchers guessed that we might subconsciously use blinks as a sort of mental resting point, to briefly shut off visual stimuli and allow us to focus our attention. To test the idea, they put 10 different volunteers in an fMRI machine and had them watch the TV show “Mr. Bean” (they had used the same show in their previous work on blinking, showing that it came at implicit break points in the video). They then monitored which areas of the brain showed increased or decreased activity when the study participants blinked.
Their analysis showed that when the Bean-watchers blinked, mental activity briefly spiked in areas related to the default network, areas of the brain that operate when the mind is in a state of wakeful rest, rather than focusing on the outside world. Momentary activation of this alternate network, they theorize, could serve as a mental break, allowing for increased attention capacity when the eyes are opened again.
To test whether this mental break was simply a result of the participants’ visual inputs being blocked, rather than a subconscious effort to clear their minds, the researchers also manually inserted “blackouts” into the video at random intervals that lasted roughly as long as a blink. In the fMRI data, though, the brain areas related to the default network weren’t similarly activated. Blinking is something more than temporarily not seeing anything.
It’s far from conclusive, but the research demonstrates that we do enter some sort of altered mental state when we blink—we’re not just doing it to lubricate our eyes. A blink could provide a momentary island of introspective calm in the ocean of visual stimuli that defines our lives.
Those just as concerned about where they’ve been as where they’re going might be keen to give the “FlyViz” a go. Created by a team of French researchers to expand the scope of human vision, the prototype system captures vision on a 360-degree camera attached to the top of a helmet that is processed in real time and displayed on Sony’s HMZ-TD Personal 3D Viewer, giving the wearer a 360-view of their surroundings.
Your beautiful eyes by Suren Manvelyan
Trabecular meshwork cells from a pig’s eye
Image by Carmen Laethem (Aerie Pharmaceuticals Research Triangle Park, North Carolina, USA)
(Source: nikonsmallworld.com)
New technique to deliver stem cell therapy may help damaged eyes regain their sight
Engineers at the University of Sheffield have developed a new technique for delivering stem cell therapy to the eye which they hope will help the natural repair of eyes damaged by accident or disease. This could help millions of people across the world retain – or even regain - their sight.
In research published in the journal Acta Biomaterialia, the team describe a new method for producing membranes to help in the grafting of stem cells onto the eye, mimicking structural features of the eye itself. The technology has been designed to treat damage to the cornea, the transparent layer on the front of the eye, which is one of the major causes of blindness in the world.
Using a combination of techniques known as microstereolithography and electrospinning, the researchers are able to make a disc of biodegradable material which can be fixed over the cornea. The disc is loaded with stem cells which then multiply, allowing the body to heal the eye naturally.
“The disc has an outer ring containing pockets into which stem cells taken from the patient’s healthy eye can be placed,” explains EPSRC Fellow, Dr Ílida Ortega Asencio, from Sheffield’s Faculty of Engineering. “The material across the centre of the disc is thinner than the ring, so it will biodegrade more quickly allowing the stem cells to proliferate across the surface of the eye to repair the cornea.”
A key feature of the disc is that it contains niches or pockets to house and protect the stem cells, mirroring niches found around the rim of a healthy cornea. Standard treatments for corneal blindness are corneal transplants or grafting stem cells onto the eye using donor human amniotic membrane as a temporary carrier to deliver these cells to the eye. For some patients, the treatment can fail after a few years as the repaired eyes do not retain these stem cells, which are required to carry out on-going repair of the cornea. Without this constant repair, thick white scar tissue forms across the cornea causing partial or complete sight loss. The researchers have designed the small pockets they have built into the membrane to help cells to group together and act as a useful reservoir of daughter cells so that a healthy population of stem cells can be retained in the eye.
Seeing the world through the eyes of an Orangutan
Dr Neil Mennie, from The University of Nottingham Malaysia Campus (UNMC), has received funding from Ministry of Science and Technology and Innovation, Malaysia (MOSTI) to study the eye movements of Tsunami — a seven year old orangutan at The National Zoo of Malaysia (Zoo Negara). Not only will Dr Mennie’s research address vital questions about the visual cognition of humans and apes in natural tasks, it will also provide valuable enrichment for the juvenile captive-born orangutan.
Dr Mennie said: “Orangutans are particularly interesting because to survive in the treetops they must be very spatially aware of their surroundings. I hope to investigate their ability to search for food and to compare their progress with humans in 3D search and foraging tasks.
Dr Mennie, who is from the Cognitive and Sensory Systems Research Group in the School of Psychology at UNMC, is interested in how humans and apes use their brains to learn and make predictions about our surroundings. With the help of Tsunami’s keeper, Mohd Sharullizam Ramli, and the special eye tracking equipment that is worn over her head and shoulders, Dr Mennie has spent the last year recording Tsunami’s eye and body movements during the performance of complex actions such as locomotion, foraging for food and manipulation of small objects.
Why older people struggle to read fine print
Psychologists from the University of Leicester have carried out unique eye tests to examine reading styles in young and old people – and discovered for the first time that the way we read words changes as we grow older.
The team from the School of Psychology used an innovative method of digitally manipulating text combined with precise measures of readers’ eye movements. This provides novel insights into how young and older adults use different visual cues during reading.
Their results have been published in the journal Psychology and Aging.
The researchers conducted experiments that used very precise measures of readers’ eye movements to assess how well they read lines of text that had been digitally manipulated to enhance the salience of different visual information. For instance, sometimes the text was blurred and other times the features of the individual letters were sharply defined.
The results showed that whereas young adults (18-30 years) found it easiest to read lines of text when the fine visual detail was present, this was more difficult for older adults (65+years), who found it easier to read more blurred text. These findings support the view that older adults use a different reading strategy from younger adults and that they rely more than young adults on holistic cues to the identities of words, such as word shape.
The research makes an important contribution to understanding why older people have difficulty in reading. The findings will promote further work to more fully understand this difficulty and already points to ways in which it can be combatted.