In the midst of the current resurgence of measles across the United States, many people may still believe it's a harmless, transient disease.
But experts warn that even before the telltale skin rash appears, the infection typically shows up in the eyes. In rare cases, measles can trigger long-term vision problems and even blindness.
Also, one or two of every 1 000 children who get measles will die from it, according to the US Centres for Disease Control and Prevention.
"It's not as simple as you get the measles and that's it," said Dr. Jonathan Song, an associate professor of ophthalmology at the Keck School of Medicine at the University of Southern California, in Los Angeles.
Severe complications from measles can include brain swelling that - along with irritation or clouding of the eye's cornea - can rob children of their sight.
Read: USA goes from measles-free to 141 cases
"Almost all people who get measles will get the red eyes called conjunctivitis," Song said. "Once they get red eyes ... they can develop inflammation of the cornea, which can break down the cornea and lead to scarring and even blindness."
The CDC reported 141 people from 17 states and Washington, D.C., were known to have measles as of February 13, and most of them had not been immunized. The vast majority of those recently infected are part of a large, ongoing multistate outbreak linked to Disneyland in California.
Measles causes up to 60,000 cases of blindness worldwide each year, according to a survey published by the U.S. National Library of Medicine. Most of those blinded by the infection are in developing nations and suffer from a vitamin A deficiency.
But regardless of nutritional status, children can develop measles-related vision complications either because their mothers contracted the virus during pregnancy, or by acquiring measles during childhood, eye experts said.
"The most common eye complications don't cause vision loss and are temporary," said Dr. Jane Edmond, a paediatric ophthalmologist at Texas Children's Hospital in Houston.
"But the rare encephalitis [brain swelling] that can occur with measles in a child can be devastating and of course, the eyes are hooked up to the brain, so another way to affect vision is through this brain-based injury," said Edmond, who is also a spokesperson for the American Academy of Ophthalmology.
Read: Overweight kids at risk of blindness
The earlier a child is infected with measles, the more likely any resulting eye damage will be lifelong, Song said. In the cornea - the clear tissue serving as the "window" into the eye - the virus can progress from inflammation and redness to scarring that blocks the clarity of images reaching the brain.
"Total vision loss depends a lot on age," Song said. "In a normal child, the visual system develops within the first four months of life, when babies are forming connections from brain to eye. So if anything is blocking the front of the eye, that can be permanent."
Vaccinations as preventative measure
Sometimes, measles infection damages or destroys cells in the retina, Song and Edmond said. The retina, which lines the back of the eye, senses light and sends signals to the brain. In rare cases, the virus even damages the optic nerve, causing potentially irreversible blindness, according to the academy of ophthalmology.
Both ophthalmologists and the academy recommend routine measles vaccinations as a way of preventing visual complications of the infection, among other serious outcomes.
About 90 to 95 percent of all vaccine-eligible people need to be immunized against measles to confer so-called "herd immunity" to others in society who cannot be immunized, public health experts say. People who should not be vaccinated include pregnant women and seriously ill children, the CDC says.
"What if you got the measles and it was no big deal, but you infected somebody for whom it was?" asked Edmond. "Yes, measles in our country doesn't have a lot of bad [outcomes], but you have to think about others."
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