Watch how doctors examine leprosy patients for signs of vision impairment

Leprosy affects the skin, eyes, and upper respiratory tract

Untreated, the disease can lead to permanent nerve damage and the loss of sensation in arms, legs, and other extremities. The exact form of transmission remains unclear, but scientists suspect it is spread via respiratory droplets over a prolonged period. (Warning: Graphic content, including photos of deformities.)

Nerve axons become damaged by leprosy, so patients may lose feeling in their skin

Infection of the peripheral nerves—nerves outside the brain and spinal cord—is a known complication of leprosy. That damage can cause patients to lose their sense of touch and the ability to feel pain or temperature in affected areas, leading to accidental injury.

Leprosy symptoms may appear 20 years after infection, so contact tracing isn't possible.

Leprosy doesn't cause fingers or toes to fall off

The nerve damage that results from infection sometimes causes loss of feeling in extremities so injuries like cuts or burns may be missed. In such cases, resulting infections can lead to digit loss. Fingers or toes can also appear to shorten with this disease because nerve damage can sometimes make muscles in fingers and toes so weak that they're reabsorbed by the body.

See examples of leprosy in the Bible—a broad term for skin ailments in ancient times

People afflicted with leprosy in the Bible may have had a range of different skin diseases, rather than what's clinically diagnosed as Hansen's disease (leprosy) today. In the Bible, as in many traditional societies, those with the disease were often considered unclean or sinful.

More than 200,000 people are diagnosed with leprosy annually

The disease still occurs in more than 120 countries. Brazil, India, and Indonesia continue to report more than 10,000 new cases annually.

Up to 225 cases of leprosy in the US are diagnosed each year

Most cases in the US are imported, meaning someone was infected in a country where it was more common. Since symptoms can sometimes take decades to appear, tracing the origin of the disease can be hard.

See what regions report new leprosy cases

This graphic shows the burden of leprosy by region for 2023, based on data provided from the World Health Organization, which collates this information. Southeast Asia leads in the number of cases by region. (Some readers may experience a paywall.)

Listen to what it was like living as a medieval leper

This podcast uses paleopathological and anthropological findings to reconstruct what it was like for people diagnosed with leprosy in medieval times on the Eurasian continent. If a town lacked a leprosarium—an isolated leper asylum or colony—or the suspected leper was a foreigner or a Jew, which would make them ineligible for leprosarium admission, they'd be expelled.

About 95% of people are naturally immune to leprosy.

Read excerpted accounts from some of the 8,000 residents with leprosy on Moloka'i

Accounts preserved by the Kalaupapa National Historical Park describe how residents felt about being sent to live in this remote location and knowing they would never be allowed to leave. In 2012, 20 residents with the disease continued to voluntarily live in the area.

America had a national leprosarium—a leper colony—in Louisiana until 1999

Public health officials forcibly sent those diagnosed with leprosy to the Louisiana Leper Home in Carville, first founded in 1894. Listen to an interview about this site, its evolution, and how its residents advocated for themselves—including regaining the right to vote.

81% of Florida's leprosy cases occur in central Florida, raising concerns

Researchers noted in 2023 that about one-fifth of new US leprosy cases were reported in the central part of the Sunshine State. What's more, about a third of the new US cases overall appear to have been acquired locally, raising questions about whether the disease is now naturally occurring in parts of the southeastern US.

Leprosy bacteria are sometimes grown on mouse feet for research since the pathogens can't be grown in a petri dish.

Recent research indicates leprosy was present in the Americas before European settlers

New research published in 2025 upended long-held notions that the disease was introduced to the Americas by European colonizers. Evidence of a lesser-known leprosy-causing bacterium was found in ancient human remains that date back 4,000 years.

Wild chimpanzees have been spotted with leprosy lesions

In research published in 2021, scientists reported discovering cases of leprosy in wild chimpanzees from Guinea-Bissau and the Ivory Coast—marking the first time the disease has been found in any nonhuman species in Africa. They confirmed that leprosy was the cause of the deformities by testing the animals' poop for the presence of the disease-causing bacteria.

Changes in vision or eye pain can be early MS symptoms

This occurs due to myelin degradation around the optic nerve, impairing its ability to transmit visual information to the brain. Individuals may especially experience eye symptoms after exercising or taking a hot shower because boosted body temperatures slow down nerve function in nerves already damaged by MS.

Leprosy bacteria replicate extremely slowly—only once every two weeks

Mycobacterium leprae has a long incubation period and a very slow replication rate, taking roughly 12 to 14 days to make a copy of itself and divide. In contrast, bacteria like E. coli can replicate in about 20 minutes in ideal conditions. Someone can be infected for years without experiencing any symptoms. This also makes the disease difficult to treat. This video describes the knowns—and unknowns—about this infectious bacterium.

Read an account of what life was like in America's national leprosarium—its leper colony

José Ramirez Jr. shares an account of his eight years at the 300-acre national leprosarium in Carville, Louisiana, from 1968 through the mid-1970s. Mostly staffed by nuns with nursing degrees, this facility was home to hundreds of people at a time, and it's also the site where they were required to be buried.

People can—and have—contracted leprosy from armadillos

A 2011 study linked multiple human cases to the handling of armadillos or the consumption of their meat. The research couldn't document direct transmission, but did find that the animals and humans shared the same exact strain of the disease.

Using brain implants to restore vision

Several companies are attempting to create brain-computer interfaces that skip over retinas and optic nerves to allow visual input to go straight to the brain, potentially restoring some sight to the blind. Clinical trial findings suggest restored sight is sparse and manifests differently than a sighted person might expect, appearing as specks of "light" clusters called phosphenes to help differentiate one's surroundings.

Lupus, an autoimmune disease with varied symptoms, was named for wolf bite-like lesions

The 13th-century physician behind the name (lupus is Latin for wolf) named it after a patient he saw who had facial lesions that looked to him like a wolf's bite. Other common symptoms of the disease include extreme fatigue, painful and swollen joints, fevers, and light sensitivity.

How MS is diagnosed with brain and spinal cord MRIs and eye tests

There's no definitive test for MS, but to make a diagnosis doctors typically use MRIs of the brain and spinal cord to hunt for telltale lesions. Also, optic nerve tests to see how quickly information travels down the optic nerve—since degraded myelin sheaths will slow electrical signals between the eye and brain.

Leprosy has been detected in British red squirrels

The animals have been infected with both strains of the bacterium that cause leprosy. Researchers have found that squirrels living in different parts of the UK were infected with different species of the disease-causing bacteria. (Some users may experience a paywall.)

In a first, eye prosthesis has restored sight to macular generation patients

In a clinical trial, 27 of 32 participants with advanced macular degeneration regained enough vision to read books, food labels, and subway signs about a year after receiving a prosthetic retina device. This is the first device to restore functional vision to patients with incurable vision loss, though in this case they can only see in black and white, with no shades in between.

During LASIK surgery, a laser removes microscopic amounts of tissue from the cornea

Before surgery, a patient’s vision needs are incorporated with measurements and mapping of their eye’s surface to identify corrections to refractive errors. This ensures light entering the eye correctly focuses onto the retina to produce a clear image.

Because the retina lacks pain receptors, during a solar eclipse, those watching without protective eyewear may suffer from permanent damage without realizing it.

Post-treatment Lyme disease syndrome may be caused by bacterial remnants in the liver

PTLDS, which refers to lingering symptoms of Lyme after antibiotic treatment, is an area of active research. Rodent research published in 2025 suggests that these ongoing symptoms may potentially be due to the body's inflammatory response to lingering cellular components from the bacteria that cause Lyme, Borrelia burgdorferi. In rodents, components of the bacteria's cellular wall may remain in the liver after the bacteria were eliminated with antibiotics.

Scientists create contact lenses that give you infrared vision

Scientists have created lenses that use nanoparticles to convert infrared light into visible light, allowing human eyes to observe previously invisible parts of the electromagnetic spectrum. This technology may help colorblind individuals by converting colors they cannot see into wavelengths they can.

Examining self-diagnosed synesthesia

A growing number of people on social media claim to have a perceptual condition that lets them smell colors, see music, or taste sounds. But do they really?

Vision experts generally don't recommend blue-light-blocking glasses because there's no scientific evidence that the light from computer screens damages eyes.

Nonwhite Lyme patients tend to be diagnosed later and have more severe disease

Peer-reviewed research published in 2025 from Pfizer—a pharmaceutical company working on a candidate vaccine for Lyme disease—examined Lyme data from more than 150,000 Medicare and Medicaid beneficiaries and found that Black patients, as compared to white beneficiaries, were more likely to have disease that had spread further throughout the body at the time of care. The difference, the scientists wrote, may be partly due to difficulties recognizing the characteristic rash on darker-colored skin.

Read a study about racial differences in Lyme disease diagnosis

The research published in September 2025 examined differences in Lyme disease diagnosis among Medicaid and Medicare beneficiaries using data from 2016 to 2021. It notes that though US Lyme disease surveillance data indicates more than 90% of diagnosed Lyme cases are among white people, people of color—particularly those who identify as Black or African American—have higher rates of more severe disease of Lyme, with symptoms including arthritis and neurologic impacts.

Measles symptoms range from fever to pneumonia and encephalitis

While less common, most measles-related deaths come from secondary conditions such as pneumonia (one to six cases per 100 patients) and encephalitis (one case per 1,000 patients). Blindness, which is rare, may arise from corneal ulceration.

In 1865, Hawaii's king authorized forcible removal, quarantining of those with leprosy

King Kamehameha V authorized the removal of anyone with leprosy symptoms and for them to be placed in a medical facility later maintained by the Catholic Church on Moloka'i, Hawaii's fifth largest island. Patients weren't allowed to transfer to other medical facilities until 1969.

Watch patient stories describing life with macular degeneration

This video series features patients discussing their experiences with the disorder, family members describing caregiving, and other insights about the disease.

What pupils can reveal about a person’s thoughts and feelings

Eyes have long been said to be the window to the soul. In this article, a psychologist and pupillometrist explores research demonstrating pupils as a window into the mind. Pupils tell us how intensely someone is exerting mental effort, or even reveal what a person is imagining. Read this article for insight into the field of pupillometry and how it can offer insights into our psyches.

One theory claims the retinae of SAD patients may fail to adjust to less light in winter

Most people’s eyes become more sensitive to light in the winter months, but some do not. This failure to adjust causes ripple effects on those individuals’ biological clocks. This Ted-ED video provides a clear, brief, narrative explanation of the condition in six minutes.

Watch the cumbersome, but necessary, precautions healthcare workers must take to care for and protect themselves while caring for Ebola patients.

Usher Syndrome, a rare genetic disorder, causes progressive hearing and vision loss, and people with the condition sometimes eventually become deaf and blind.

Corrective vision technologies rely on the bending of light waves

When focusing on an object, muscles change the shape of the lens, which refracts incoming light such that it focuses at the retina. If the cornea is unable to bend light correctly, lenses or contact lenses can provide supplemental refraction to ensure a focused image is produced.

Erythema migrans rash is common in Lyme—but it often doesn't look like a bull's-eye

The US Centers for Disease Control and Prevention states that this rash occurs in roughly 70% or more of Lyme disease patients, and typically occurs at the site of a tick bite. The rash may expand slowly over several days and feel warm to the touch, but it's rarely itchy or painful. As it grows, areas of it may clear—creating a target or "bull's-eye" appearance.

The origin of LASIK eye surgery, from a lab incident to federal funding and widespread use

After a University of Michigan engineering student suffered retinal burns from an ultrashort pulse laser, researchers realized it could be used to reshape the cornea and improve a person's vision with greater precision than a scalpel and earlier laser technologies. Agencies, including the National Science Foundation, the National Institutes of Health, and the Department of Energy, provided funding to develop and commercialize the procedure.

An overview of modern clinical research on LSD

Researchers have determined that LSD, taken in a medical setting, decreases anxiety related to "life-threatening disease," reduces brain reactivity to fearful faces, increases the meaning and emotional response derived from music, and more. No complications of LSD administration have been observed in medical settings, though acute adverse effects, including exhaustion, nausea, and difficulty concentrating.

As deposits build up under the eye, the retina bends with macular degeneration

The retina bends due to the accumulation of proteins and other materials beneath it. That's considered the milder "dry" form of macular degeneration. Another form, called "wet" macular degeneration, is caused by abnormal blood vessels leaking fluid into the eye, which can rapidly affect central vision.

Why surgeons implant teeth into eyes

What if the thing that restored your vision… was your own tooth? That’s exactly what happened to Brent Chapman. After 20 years without sight, a bizarre surgery using his tooth as a lens restored his vision.

New eye implant clinical trial recruiting in 2026

University of Southern California researchers have launched a phase 2b clinical trial of a stem cell implant designed to restore vision in people with advanced dry macular degeneration. Patients will be randomized to receive the stem cell implant or a simulated procedure and placebo implant. This type of larger, second-stage clinical trial is designed to confirm efficacy and dosing and to look for side effects. It's one of the stages that precedes the US Food & Drug Administration approval of a device.

Studying involuntary, rapid eye movements is a key part of vertigo diagnosis

A doctor will look at a vertigo patient's rapid, uncontrollable eye movements—formally called nystagmus—to better understand its causes. When a patient is lying down with their head turned and their eyes spin in a certain position and stop it's likely a peripheral cause, but if the spinning doesn't stop or it changes direction it's more likely a central nervous system issue.

Dogs' disease-sniffing skills were first identified in 1989

This capability, reported in the medical journal The Lancet, was discovered when a dog reportedly detected cancer in its handler. The dog repeatedly focused on a spot on the owner's leg where a malignant melanoma lesion was later found, helping lead to an early diagnosis.

Restoring vision in impaired patients via CRISPR

Since CRISPR was revealed as a gene editing tool in 2012, it has been on an accelerated track to real-world applications. Among other clinical demonstrations, doctors have now injected a CRISPR treatment directly into eye cells, helping vision-impaired patients see shapes and colors again.