This cautionary tale could get your kids to eat their veggies.

A British teenager described as a “fussy eater” went blind and partially deaf after noshing nothing but potato chips, sausages, French fries and white bread for the past decade, according to an alarming case study published in the Annals of Internal Medicine over the weekend.

The 17-year-old, who wasn’t named in the report, had visited a general practitioner three years earlier complaining of fatigue. Tests at that time revealed he was anemic and had low levels of the vitamin B12, so he began taking vitamin injections and receiving diet advice. But his height and BMI were normal, so doctors didn’t suspect any greater nutritional issues.

By the time he was 15, however, his vision and hearing had begun to deteriorate. Now at 17, he has suffered permanent vision loss, partial hearing loss, as well as bone weakness. So researchers at the University of Bristol examined his case. And after ruling out factors such as his BMI, family history, medications, or drug and alcohol use, they determined that his poor diet had damaged his optic nerve badly enough to cause blindness.

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In fact, he had developed a condition known as nutritional optic neuropathy (NON), which is more common in countries where extreme poverty, drought and war have led to widespread hunger and malnutrition. (Cuba suffered an epidemic of optic and peripheral neuropathy that affected more than 50,000 people in the early 1990s, where nutritional deficiencies were a key factor.) Further tests determined he still had a vitamin B12 deficiency, plus low copper and selenium levels, as well as “markedly reduced” vitamin D and bone mineral density levels. (These vital nutrients are found in lean beef and poultry, fatty fish, leafy green vegetables, dairy products, eggs, nuts and seeds, and other parts of a healthy, balanced diet.)

Upon questioning him about his daily dining habits, they learned that he ate French fries from the local fish and chips shop every day. He had also been living on Pringles chips, white bread, processed ham slices and sausages since he was in elementary school, because he didn’t like foods with certain textures. This led the researchers to also diagnose him with avoidant-restrictive food intake disorder, or AFRID, which is a relatively new diagnosis that describes subjects who are sensitive to the taste, texture, smell and appearance of certain types of food, or when someone shows a lack of interest in food. They noted that in many AFRID cases, as in this one, the patient has what’s considered a normal BMI, so the issue isn’t always obvious.

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About two billion people worldwide are affected by nutritional deficiencies. In high-income countries like the U.S. and the U.K., however, they are usually caused by bowel problems (like celiac disease and Crohn’s disease) that mess with the absorption of important nutrients into the stomach, or drug use, or poor diet combined with alcoholism or smoking. It’s rare for purely dietary causes to lead to nutritional optic neuropathy in developed countries, although the researchers warned this kind of condition could become more common as more consumers choose junk food over more nutritious food, or as the rise of veganism (which cuts out fish, meat, eggs and dairy) leads to some people not getting enough vitamin D or B12 in their diets if they aren’t supplementing properly.

“Vitamins play a very important role in maintaining eye health,” Dr. Valerie Elmalem, a neuro-ophthalmologist at New York Eye and Ear Infirmary of Mount Sinai, told MarketWatch. These nutrients include vitamin A found in orange foods like carrots and mangoes, which keep the surface of the eye moist and aid in night vision. But B vitamins, iron and thiamine (found in beef, liver, nuts, oranges, eggs and fortified rice, bread, cereal and pasta) are also vital.

“You can get a thiamine deficiency in as quickly as three weeks, which can also affect the optic nerve, the way the eyes move around, and it can also affect your memory,” she said. “I think several years of this [teen’s] type of diet would certainly produce deficiencies severe enough to cause vision loss.”

The damage to the eye can be reversed if nutritional optic neuropathy is caught early, but it was too late in this teen’s case. The decade of a highly-processed diet packed with added salt, sugar and refined carbohydrates had taken its toll. (Pringles owner Kellogg K, +0.68% did not respond to a MarketWatch request for comment by presstime.)

“Our vision has such an impact on quality of life, education, employment, social interactions, and mental health. This case highlights the impact of diet on visual and physical health, and the fact that calorie intake and BMI are not reliable indicators of nutritional status,” wrote lead author Dr. Denize Atan, a clinical lead for neuro-ophthalmology at Bristol Eye Hospital, in a statement. Her team is encouraging clinicians to consider nutritional neuropathy in any patients with unexplained vision problems and poor diet, regardless of their BMI. (After all, this patient’s BMI had been normal, so it wasn’t obvious that he was malnourished.)

Dr. Atan also wrote in an accompanying article that not getting enough B vitamins, iron, calcium, magnesium and copper are all known to cause optic neuropathy, and “are easily misdiagnosed as other disorders if the doctor doesn’t have the patient’s dietary history.”

But your vision isn’t the only reason to watch what you eat. The USDA warns that about half of all American adults have one or more chronic disease — including diabetes, obesity and cardiovascular disease — that are often related to poor diet. Read the USDA’s dietary guidelines for Americans, including questions about caffeine, cholesterol and fat, here.

And if you are concerned that you or someone you know has an eating disorder, visit the National Eating Disorders Association website, or call the helpline at (800) 931-2237.