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Visualizing the Evolution of Vision and the Eye

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Roadmapping the Evolution of the Eye

Throughout history, numerous creatures have evolved increasingly complex eyes in response to different selective pressures.

Not all organisms, however, experience the same pressures. It’s why some creatures today still have eyes that are quite simple, or why some have no eyes at all. These organisms exemplify eyes that are “frozen” in time. They provide snapshots of the past, or “checkpoints” of how the eye has transformed throughout its evolutionary journey.

Scientists study the genes, anatomy, and vision of these creatures to figure out a roadmap of how the eye came to be. And so, we put together an evolutionary graphic timeline of the eye’s different stages using several candidate species.

Let’s take a look at how the eye has formed throughout time.

Where Vision Comes From

The retina is a layer of nerve tissue, often at the back of the eye, that is sensitive to light.

When light hits it, specialized cells called photoreceptors transform light energy into electrical signals and send them to the brain. Then the brain processes these electrical signals into images, creating vision.

The earliest form of vision arose in unicellular organisms. Containing simple nerve cells that can only distinguish light from dark, they are the most common eye in existence today.

The ability to detect shapes, direction, and color comes from all of the add-ons evolution introduces to these cells.

Two Major Types of Eyes

Two major eye types are dominant across species. Despite having different shapes or specialized parts, improved vision in both eye types is a product of small, gradual changes that optimize the physics of light.

Simple Eyes

Simple eyes are actually quite complex, but get their name because they consist of one individual unit.

Some mollusks and all of the higher vertebrates, like birds, reptiles, or humans, have simple eyes.

Grid of photos showing examples of simple eyes in the animal kingdom

Simple eyes evolved from a pigment cup, slowly folding inwards with time into the shape we recognize today. Specialized structures like the lens, cornea, and pupil arose to help improve the focus of light on the retina. This helps create sharper, clearer images for the brain to process.

Simple eye evolution

Compound Eyes

Compound eyes are formed by repeating the same basic units of photoreceptors called ommatidia. Each ommatidium is similar to a simple eye, composed of lenses and photoreceptors.

Grouped together, ommatidia form a geodesic pattern that is commonly seen in insects and crustaceans.

Grid of photos showing examples of compound eyes in the animal kingdom

Our understanding of the evolution of the compound eye is a bit murky, but we know that rudimentary ommatidia evolved into larger, grouped structures that maximize light capture.

compound eye evolution

In environments like caves, the deep subsurface, or the ocean floor where little to no light exists, compound eyes are useful for producing vision that gives even the slightest advantage over other species.

How Will Vision Evolve?

Our increasing dependency on technology and digital devices may be ushering in the advent of a new eye shape.

The muscles around the eye stretch to shift the lens when staring at something close by. The eye’s round shape elongates in response to this muscle strain.

Screen time with cellphones, tablets, and computers has risen dramatically over the years, especially during the COVID-19 pandemic. Recent studies are already reporting rises in childhood myopia, the inability to see far away. Since the pandemic, cases have increased by 17%, affecting almost 37% of schoolchildren.

Other evolutionary opportunities for our eyes are currently less obvious. It remains to be seen whether advanced corrective therapies, like corneal transplants or visual prosthetics, will have any long-term evolutionary impact on the eye.

For now, colored contacts and wearable tech may be our peek into the future of vision.

Complete Sources

Fernald, Russell D. “Casting a Genetic Light on the Evolution of Eyes.” Science, vol. 313, no. 5795, 29 Sept. 2006, pp. 1914–1918

Gehring, W. J. “New Perspectives on Eye Development and the Evolution of Eyes and Photoreceptors.” Journal of Heredity, vol. 96, no. 3, 13 Jan. 2005, pp. 171–184. Accessed 18 Dec. 2019.

The Evolution of Sight | PHOS.”

Land, Michael F, and Dan-Eric Nilsson. Animal Eyes. Oxford ; New York, Oxford University Press, 2002.

“The Major Topics of the Research Work of Prof. Dan-E. Nilsson: Vision-Research.eu – the Gateway to European Vision Research.” Accessed 3 Oct. 2022.

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Older patients, non-English speakers more likely to be harmed in hospital: report

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Patients who are older, don’t speak English, and don’t have a high school education are more likely to experience harm during a hospital stay in Canada, according to new research.

The Canadian Institute for Health Information measured preventableharmful events from 2023 to 2024, such as bed sores and medication errors,experienced by patients who received acute care in hospital.

The research published Thursday shows patients who don’t speak English or French are 30 per cent more likely to experience harm. Patients without a high school education are 20 per cent more likely to endure harm compared to those with higher education levels.

The report also found that patients 85 and older are five times more likely to experience harm during a hospital stay compared to those under 20.

“The goal of this report is to get folks thinking about equity as being a key dimension of the patient safety effort within a hospital,” says Dana Riley, an author of the report and a program lead on CIHI’s population health team.

When a health-care provider and a patient don’t speak the same language, that can result in the administration of a wrong test or procedure, research shows. Similarly, Riley says a lower level of education is associated with a lower level of health literacy, which can result in increased vulnerability to communication errors.

“It’s fairly costly to the patient and it’s costly to the system,” says Riley, noting the average hospital stay for a patient who experiences harm is four times more expensive than the cost of a hospital stay without a harmful event – $42,558 compared to $9,072.

“I think there are a variety of different reasons why we might start to think about patient safety, think about equity, as key interconnected dimensions of health-care quality,” says Riley.

The analysis doesn’t include data on racialized patients because Riley says pan-Canadian data was not available for their research. Data from Quebec and some mental health patients was also excluded due to differences in data collection.

Efforts to reduce patient injuries at one Ontario hospital network appears to have resulted in less harm. Patient falls at Mackenzie Health causing injury are down 40 per cent, pressure injuries have decreased 51 per cent, and central line-associated bloodstream infections, such as IV therapy, have been reduced 34 per cent.

The hospital created a “zero harm” plan in 2019 to reduce errors after a hospital survey revealed low safety scores. They integrated principles used in aviation and nuclear industries, which prioritize safety in complex high-risk environments.

“The premise is first driven by a cultural shift where people feel comfortable actually calling out these events,” says Mackenzie Health President and Chief Executive Officer Altaf Stationwala.

They introduced harm reduction training and daily meetings to discuss risks in the hospital. Mackenzie partnered with virtual interpreters that speak 240 languages and understand medical jargon. Geriatric care nurses serve the nearly 70 per cent of patients over the age of 75, and staff are encouraged to communicate as frequently as possible, and in plain language, says Stationwala.

“What we do in health care is we take control away from patients and families, and what we know is we need to empower patients and families and that ultimately results in better health care.”

This report by The Canadian Press was first published Oct. 17, 2024.

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.

The Canadian Press. All rights reserved.

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Alberta to launch new primary care agency by next month in health overhaul

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CALGARY – Alberta’s health minister says a new agency responsible for primary health care should be up and running by next month.

Adriana LaGrange says Primary Care Alberta will work to improve Albertans’ access to primary care providers like family doctors or nurse practitioners, create new models of primary care and increase access to after-hours care through virtual means.

Her announcement comes as the provincial government continues to divide Alberta Health Services into four new agencies.

LaGrange says Alberta Health Services hasn’t been able to focus on primary health care, and has been missing system oversight.

The Alberta government’s dismantling of the health agency is expected to include two more organizations responsible for hospital care and continuing care.

Another new agency, Recovery Alberta, recently took over the mental health and addictions portfolio of Alberta Health Services.

This report by The Canadian Press was first published Oct. 15, 2024.

The Canadian Press. All rights reserved.

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Experts urge streamlined, more compassionate miscarriage care in Canada

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Rana Van Tuyl was about 12 weeks pregnant when she got devastating news at her ultrasound appointment in December 2020.

Her fetus’s heartbeat had stopped.

“We were both shattered,” says Van Tuyl, who lives in Nanaimo, B.C., with her partner. Her doctor said she could surgically or medically pass the pregnancy and she chose the medical option, a combination of two drugs taken at home.

“That was the last I heard from our maternity physician, with no further followup,” she says.

But complications followed. She bled for a month and required a surgical procedure to remove pregnancy tissue her body had retained.

Looking back, Van Tuyl says she wishes she had followup care and mental health support as the couple grieved.

Her story is not an anomaly. Miscarriages affect one in five pregnancies in Canada, yet there is often a disconnect between the medical view of early pregnancy loss as something that is easily managed and the reality of the patients’ own traumatizing experiences, according to a paper published Tuesday in the Canadian Medical Association Journal.

An accompanying editorial says it’s time to invest in early pregnancy assessment clinics that can provide proper care during and after a miscarriage, which can have devastating effects.

The editorial and a review of medical literature on early pregnancy loss say patients seeking help in emergency departments often receive “suboptimal” care. Non-critical miscarriage cases drop to the bottom of the triage list, resulting in longer wait times that make patients feel like they are “wasting” health-care providers’ time. Many of those patients are discharged without a followup plan, the editorial says.

But not all miscarriages need to be treated in the emergency room, says Dr. Modupe Tunde-Byass, one of the authors of the literature review and an obstetrician/gynecologist at Toronto’s North York General Hospital.

She says patients should be referred to early pregnancy assessment clinics, which provide compassionate care that accounts for the psychological impact of pregnancy loss – including grief, guilt, anxiety and post-traumatic stress.

But while North York General Hospital and a patchwork of other health-care providers in the country have clinics dedicated to miscarriage care, Tunde-Byass says that’s not widely adopted – and it should be.

She’s been thinking about this gap in the Canadian health-care system for a long time, ever since her medical training almost four decades ago in the United Kingdom, where she says early pregnancy assessment centres are common.

“One of the things that we did at North York was to have a clinic to provide care for our patients, and also to try to bridge that gap,” says Tunde-Byass.

Provincial agency Health Quality Ontario acknowledged in 2019 the need for these services in a list of ways to better manage early pregnancy complications and loss.

“Five years on, little if any progress has been made toward achieving this goal,” Dr. Catherine Varner, an emergency physician, wrote in the CMAJ editorial. “Early pregnancy assessment services remain a pipe dream for many, especially in rural Canada.”

The quality standard released in Ontario did, however, prompt a registered nurse to apply for funding to open an early pregnancy assessment clinic at St. Joseph’s Healthcare Hamilton in 2021.

Jessica Desjardins says that after taking patient referrals from the hospital’s emergency room, the team quickly realized that they would need a bigger space and more people to provide care. The clinic now operates five days a week.

“We’ve been often hearing from our patients that early pregnancy loss and experiencing early pregnancy complications is a really confusing, overwhelming, isolating time for them, and (it) often felt really difficult to know where to go for care and where to get comprehensive, well-rounded care,” she says.

At the Hamilton clinic, Desjardins says patients are brought into a quiet area to talk and make decisions with providers – “not only (from) a physical perspective, but also keeping in mind the psychosocial piece that comes along with loss and the grief that’s a piece of that.”

Ashley Hilliard says attending an early pregnancy assessment clinic at The Ottawa Hospital was the “best case scenario” after the worst case scenario.

In 2020, she was about eight weeks pregnant when her fetus died and she hemorrhaged after taking medication to pass the pregnancy at home.

Shortly after Hilliard was rushed to the emergency room, she was assigned an OB-GYN at an early pregnancy assessment clinic who directed and monitored her care, calling her with blood test results and sending her for ultrasounds when bleeding and cramping persisted.

“That was super helpful to have somebody to go through just that, somebody who does this all the time,” says Hilliard.

“It was really validating.”

This report by The Canadian Press was first published Oct. 15, 2024.

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.

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