Is measles a leading cause of child blindness around the world?

An assertion from Sen. Rand Paul, R-Ky., that vaccinations are about freedom and should be left to parental choice spawned a raft of reaction from the pundit and political world.

One claim we heard a lot is Paul should know better. After all, he is an eye surgeon.

In an interview on CNBC on Feb. 2, 2015, Paul hailed vaccines as a medical triumph but said he sees the controversy of whether it should be mandatory as an "issue of freedom." Further, he said he heard of many "tragic cases of walking, talking, normal children who wound up with profound mental disorders after vaccines."

Dr. Celine Gounder, a physician who frequently appears on news channels to analyze health news, addressed his comments on CNN Newsroom the following day.

"Frankly, Rand Paul as an ophthalmologist should be out there saying measles is one of the most common causes of child blindness worldwide," Gounder said. "And as an eye doctor, he should be advocating for measles vaccination for that reason."

Gounder’s claim, as it relates to Paul’s life as an eye surgeon, got our attention.

And it’s correct. Gounder’s point is backed up by sources such as the World Health Organization and a host of academic studies and review papers that she sent us.

‘Worldwide’ is key

Conjunctivitis, or pink eye, is a common side effect of a measles infection.

"Whoever you are, wherever you are," people with measles can’t stand bright sunlight, said Dr. James Cherry, a pediatric infectious disease expert at the University of California, Los Angeles.

But for children in poor countries, eye damage from measles can be much worse.

Blindness by measles in children is not common across North America and Europe, areas with high vaccination rates and access. The leading causes of blindness in those continents are lesions of the optic nerve, according to the WHO.

In low-income countries, where access to vaccines that prevent measles is limited and malnutrition is prevalent, corneal scarring from measles and a deficiency of vitamin A are the major causes.

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In the United States, based on the most recent CDC data from more than 20 years ago, the leading complication (and complications from measles of any sort in the U.S. are not common) was diarrhea followed by middle ear inflammation and pneumonia.

"In the U.S., children could potentially develop eye problems during an episode of measles if they are malnourished," said Dr. Richard Semba, Johns Hopkins University School of Medicine ophthalmology professor. "This would probably be rare."

Vitamin A is important for eyes to function as they should, as well as for the body’s immune system and growth. If your teacher or mom didn’t tell you, the vitamin is found in eggs, whole milk, butter and liver, as well as leafy green vegetables and red, orange and yellow fruits.

Measles is most common in countries of sub-Saharan Africa, southeast Asia and south Asia, together home to 85 percent of all blind children. In these places, measles is endemic, according to a 2004 review paper by Semba. That paper found measles blindness accounted for anywhere from 15,000 to 60,000 cases of child blindness per year.

Here's how Semba explained blindness happening from contracting the highly contagious measles virus:

The cornea, the front transparent layer of the eye, requires vitamin A to work. The retina, which is the back layer of the eye that receives visual images (like the film in a camera), requires vitamin A in order to allow us to see at night.

A measles infection can reduce the levels of vitamin A that the body needs for normal health. As a result, during a measles episode, a child can develop ulcers in the cornea during a measles episode that makes it hard to see at night. The end result is "a devastating loss of vision and blindness," Semba said.

Dryness in corneas can result in night blindness, corneal ulceration, scarring and resulting blindness, studies show.

Countries with vaccination programs for measles have reduced the problem of widespread eye disease, according to WHO. The organization also recommends that children in developing countries who contract measles receive two doses of vitamin A supplements a day apart.

"Vitamin A supplements have been shown to reduce the number of deaths from measles by 50 percent," WHO says.

Paul’s spokesman sent us a link to a New York Times reporter’s account of watching Paul get his Hepatitis A booster shot Feb. 3, 2015, but did not answer our questions.

Our ruling

Gounder suggested Paul should be singing a different tune about vaccinations, one that mentions, "Measles is one of the most common causes of child blindness worldwide."

She was careful to say worldwide. In developed countries, measles does not typically lead to blindness. But in low-income countries, it is certainly one of the leading drivers of blindness in children, experts agree.

We rate the claim True.