Tag: retina

Retinal Cells a Haven for Ebola and Other Viruses

Credit: National Eye Institute

A specific cell within the retina, the retinal pigment epithelial cell, appears to be particularly good at housing Ebola and other viruses, according to new research published in the journal Frontiers in Virology.

“Inflammation of the eye, known as uveitis, is very common following infection with Ebola and we know the cells within the iris, at the front of the eye, as well as the retina have the capacity to play a major role in uveitis and act as hosts for microorganisms,” explained study senior author Professor Justine Smith at Flinders University.

“However, what we didn’t know was which out of the two was most responsible in the case of Ebola.”

“Patients with Ebola eye disease have characteristic retinal scars”

Professor Justine Smith

The study used cells from human eyes donated from the South Australia Eye Bank to investigate the ability of iris and retinal pigment epithelial cells to be infected by Ebola.

Cells were infected with Ebola virus, Reston virus (a type of ebolavirus that does not cause disease in humans) or Zika virus (another type of virus, but one that also can cause uveitis), while some were left uninfected for the duration of the trial.

While both types of cells allow replication of the Ebola virus, it was the retinal cells that showed much higher levels of infection.

“We also found similar results when looking at the cells infected with Reston virus and Zika virus,” said Professor Smith.

“Patients with Ebola eye disease have characteristic retinal scars, suggesting the retinal pigment epithelium is involved in the disease, so this finding is consistent with what eye doctors are seeing in the clinic.

“These retinal cells are good at eating things – called phagocytosis – and they play an essential part in the visual cycle by recycling our photoreceptors, so it makes sense that these cells would be a receptive haven for Ebola, as well as other viruses.”

The researchers say the study demonstrates an important target cell for Ebola infection in the eye and suggests the potential for these cells to be monitored during acute viral infection to identify patients at highest risk of uveitis.

“Amongst other issues, including pain and blurred vision, uveitis can ultimately lead to vision loss, so it’s important we find ways to diagnose it as early as possible to enable swift treatment,” said Professor Smith.

Source: Flinders University

Retinal Scans May be Able to Detect ASD and ADHD

Eye
Source: Daniil Kuzelev on Unsplash

By measuring the electrical activity of the retina in responses to a light stimulus, researchers found that they may be able to neurodevelopmental disorders such as ASD and ADHD, as reported in new research published in Frontiers in Neuroscience.

In this groundbreaking study, researchers found that recordings from the retina could identify distinct signals for both Attention Deficit Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) providing a potential biomarker for each condition.

Using the ‘electroretinogram’ (ERG) – a diagnostic test that measures the electrical activity of the retina in response to a light stimulus – researchers found that children with ADHD showed higher overall ERG energy, whereas children with ASD showed less ERG energy.

Research optometrist at Flinders University, Dr Paul Constable, said the preliminary findings indicate promising results for improved diagnoses and treatments in the future.

“ASD and ADHD are the most common neurodevelopmental disorders diagnosed in childhood. But as they often share similar traits, making diagnoses for both conditions can be lengthy and complicated,” Dr Constable says.

“Our research aims to improve this. By exploring how signals in the retina react to light stimuli, we hope to develop more accurate and earlier diagnoses for different neurodevelopmental conditions.

“Retinal signals have specific nerves that generate them, so if we can identify these differences and localise them to specific pathways that use different chemical signals that are also used in the brain, then we can show distinct differences for children with ADHD and ASD and potentially other neurodevelopmental conditions.”

“This study delivers preliminary evidence for neurophysiological changes that not only differentiate both ADHD and ASD from typically developing children, but also evidence that they can be distinguished from each other based on ERG characteristics.”

According to the World Health Organization, one in 100 children has ASD, with 5–8% of children diagnosed with ADHD.

Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental condition characterised by being overly active, struggling to pay attention, and difficulty controlling impulsive behaviours. Autism spectrum disorder (ASD) is also a neurodevelopmental condition where children behave, communicate, interact, and learn in ways that are different from most other people.

Co-researcher and expert in human and artificial cognition at the University of South Australia, Dr Fernando Marmolejo-Ramos, says the research has potential to extend across other neurological conditions.

“Ultimately, we’re looking at how the eyes can help us understand the brain,” Dr Marmolejo-Ramos says.

“While further research is needed to establish abnormalities in retinal signals that are specific to these and other neurodevelopmental disorders, what we’ve observed so far shows that we are on the precipice of something amazing.

“It is truly a case of watching this space; as it happens, the eyes could reveal all.”

Source: Flinders University

Cell Fusion Jump-starts Retinal Regeneration

Genetics
Image source: Pixabay

Researchers have reported that they have successfully fused human retinal cells with adult stem cells, in a novel potential regenerative therapy to treat retinal damage and visual impairment.

The resulting hybrid cells stimulate the regenerative potential of human retinal tissue, something previously only thought to be found in cold-blood vertebrates.

Cell fusion events, where two different cells combine into one single entity, are known to be a possible mechanism contributing to tissue regeneration. These cell fusions result in four sets of chromosomes instead of the usual two. Though a rare phenomenon in humans, it has been reliably detected in the liver, brain, and gastrointestinal tract. Now, cell fusion events have been found also take place in the human retina, as reported in eBioMedicine.

Seeking to see if cell fusion events could differentiate into neurons, the researchers fused Müller glia, cells that play a secondary but important role in maintaining the structure and function of the retina, with adult stem cells.

“We were able to carry out cell fusion in vitro, creating hybrid cells. Importantly, the process was more efficient in the presence of a chemical signal transmitted from the retina in response to damage, resulting in rates of hybridisation increasing twofold. This gave us an important clue for the role of cell fusion in the retina,” said first author Sergi Bonilla.

The hybrid cells were injected into a growing retinal organoid, a model that closely resembles the function of the human retina. The researchers found that the hybrid cells successfully engrafted into the tissue and differentiated into cells that closely resemble ganglion cells, a type of neuron essential for vision.

“Our findings are important because they show that the Müller Glia in the human retina have the potential to regenerate neurons,” said lead researcher Professor Pia Cosma. “Salamanders and fish can repair damage caused to the retina thanks to their Müller glia, which differentiate into neurons that rescue or replace damaged neurons. Mammalian Müller glia have lost this regenerative capacity, which means retinal damage or degradation can lead to visual impairment for life. Our findings bring us one step closer to recovering this ability.”

Further work will be to understand why these hybrid cells, which have four complete sets of chromosomes, don’t result in chromosomal instability and cancer development. The authors of the study believe the retina may have a mechanism regulating chromosome segregation similar to the liver, which contains tetraploid cells that act as a genetic reservoir, undergoing mitosis in response to stress and injury.

Source: Center for Genomic Regulation

Bionic Eye Demonstration Paves the Way to Human Trials

The Phoenix99 Bionic Eye. Credit: University of Sydney

A bionic eye under development has shown to be safe and stable for long-term implantation in a three-month animal study, paving the way towards human trials.

The Phoenix99 Bionic Eye, being developed by University of Sydney and UNSW, is an implantable system, designed to restore a form of vision to patients living with severe vision impairment and blindness caused by degenerative diseases, such as retinitis pigmentosa. The device consists of two main implants: a stimulator attached to the eye and a communication module positioned under the skin behind the ear.

Published in Biomaterials, the researchers used a sheep model to observe how the body responds and heals when implanted with the device, with the results allowing for further refinement of the surgical procedure. The biomedical research team is now confident the device could be trialled in human patients and have applied for ethical approval.

The Phoenix99 Bionic Eye works by stimulating the retina which, in healthy eyes, the cells in one of the layers turn incoming light into electrical messages. In some retinal diseases, the cells responsible for this crucial conversion degenerate, causing vision impairment. The system bypasses these malfunctioning cells by stimulating the remaining cells directly, effectively tricking the brain into believing that light was sensed.

“Importantly, we found the device has a very low impact on the neurons required to ‘trick’ the brain. There were no unexpected reactions from the tissue around the device and we expect it could safely remain in place for many years,” said Mr Samuel Eggenberger, a biomedical engineer who is completing his doctorate with Head of School of Biomedical Engineering Professor Gregg Suaning.

“Our team is thrilled by this extraordinary result, which gives us confidence to push on towards human trials of the device. We hope that through this technology, people living with profound vision loss from degenerative retinal disorders may be able to regain a useful sense of vision,” said Mr Eggenberger.

Professor Gregg Suaning said the positive results are a significant milestone for the Phoenix99 Bionic Eye.

“This breakthrough comes from combining decades of experience and technological breakthroughs in the field of implantable electronics,” said Prof Suaning.

A patient is implanted with the Phoenix99, and a stimulator is positioned on the eye and a communication module implanted behind the ear. A tiny camera attached to glasses captures the visual scene in front of the wearer, and the images are processed into a set of stimulation instructions which are sent wirelessly through to the communication module of the prosthesis.

The implant then transfers the instructions to the stimulation module, which delivers electrical impulses to the neurons of the retina. The electrical impulses, delivered in patterns matching the images recorded by the camera, trigger neurons which forward the messages to the brain, which interprets the signals as seeing the scene.

Source: University of Sydney

Scientists Discover New Type of Neuron in the Retina

Source: Daniil Kuzelev on Unsplash

University of Utah scientists have discovered a new type of neuron in the retina, which will help fill in our understanding of how sensory information is relayed.

In the central nervous system a complex network of neurons communicate with each other to relay sensory and motor information. In this chain of communication, a type of neuron called interneurons serve as intermediaries . A research team led by Ning Tian, PhD, identified a previously unknown type of interneuron in the mammalian retina. Their findings were published in the journal PNAS.

This discovery is a major step forward for the field as scientists strive to build a better understanding of the central nervous system by identifying all classes of neurons and their connections.

“Based on its morphology, physiology, and genetic properties, this cell doesn’t fit into the five classes of retinal neurons first identified more than 100 years ago,” said Dr Tian. “We propose they might belong to a new retinal neuron class by themselves.”

The research team called their discovery the Campana cell after its shape, which resembles a hand bell. Campana cells relay visual signals from both types of light-sensing rod and cone photoreceptors in the retina, however their exact purpose is the subject of ongoing research. Experiments revealed that Campana cells remain activated for an unusually long time – as long as 30 seconds – in response to a 10 millisecond light flash stimulation.

“In the brain, persistent firing cells are believed to be involved in memory and learning,” said Dr Tian. “Since Campana cells have a similar behaviour, we theorise they could play a role in prompting a temporal ‘memory’ of a recent stimulation.”

Source: University of Utah

Central Retinal Artery Occlusion Needs to be Treated as A Stroke

The American Heart Association published a new scientific statement, “Management of Central Retinal Artery Occlusion,” which laid out the best methods to treat what is effectively a small stroke in the eye.

A central retinal artery occlusion (CRAO) is a rare (1 in 100 000 people) form of acute ischaemic stroke arising from a blockage of blood flow to the main artery of the eye. It causes painless, immediate vision loss in the impacted eye from which less than 20% of people will recover from.

“Central retinal artery occlusion is a cardiovascular problem disguised as an eye problem. It is less common than stroke affecting the brain but is a critical sign of ill health and requires immediate medical attention,” said the chair of the statement writing committee Brian C Mac Grory, MBBCh, BAO, MRCP, an assistant professor of neurology and staff neurologist at the Duke Comprehensive Stroke Center at Duke University School of Medicine. “Unfortunately, a CRAO is a warning sign of other vascular issues, so ongoing follow-up is critical to prevent a future stroke or heart attack.”

In a comprehensive review of the literature, committee members from a variety of specialties summarised the state of the science in this condition. They noted that a lack of clinical trials results in physicians not recognising the problem, including that it is a type of stroke, resulting in inaction and differing methods of diagnosis and treatment.

“We know acute CRAO is a medical emergency requiring early recognition and triage to emergency medical treatment,” said Dr Mac Grory. “There is a narrow time window for effective treatment of CRAO and a high rate of serious related illness. So, if a person is diagnosed in a doctor’s office or another outpatient clinic, they should be immediately sent to a hospital emergency department for further evaluation and treatment.”

CRAOs can be caused by problems with carotid arteries, the blood vessels in the neck, but there is also evidence CRAOs could be caused by heart problems such as atrial fibrillation.

CRAO risk factors include age and the presence of cardiovascular risk factors such as type 2 diabetes, smoking, and obesity. 

Currently, the literature suggests that intravenous tissue plasminogen activator (tPA) treatment, a “clot buster” also used for brain strokes, could be effective. However, to be effective and safe tPA must be administered within 4.5 hours of the onset of symptoms

Hyperbaric oxygen and intra-arterial alteplase, were also noted as showing potential but requiring further study. Hyperbaric oxygen can result in an improvement if done within 24 hours of the CRAO event. Other possible treatments needing further research icnclude breaking up clots with novel thrombolytics and using novel neuroprotectants (substances capable of preserving brain function and structure) in concert with other treatments to restore blood flow in the blocked artery.

Since there is potential for future strokes or even heart attacks, patients should undergo screening and treatment of vascular risk factors as a matter of urgency. CRAOs are complex to treat and manage, requiring the joint effort of a team of specialists.

Secondary prevention (including monitoring for complications) must be a collaborative effort between neurologists, ophthalmologists, cardiologists and primary care clinicians. Risk factor modification includes lifestyle and pharmacological interventions.

Source: News-Medical.Net

Journal information: Grory, B. M., et al. (2021) Management of Central Retinal Artery Occlusion: A Scientific Statement From the American Heart Association. Stroke. doi.org/10.1161/STR.0000000000000366.