A UK teenager’s diet of potato chips and other junk foods led to shocking health consequences, according to a new case report out this week. The boy’s doctors described how his disordered “fussy” eating led to chronic nutritional deficiencies that left him with a variety of symptoms, including permanent partial blindness.

According to the case report, published Monday in the Annals of Internal Medicine, the boy had visited his family doctor at age 14 with complaints of fatigue. He seemed otherwise healthy and wasn’t taking any medications, but he described himself as a “fussy eater” and tests showed that he was low in vitamin B12 and had anemia. He was prescribed injections of B12 and was given advice on how to eat a proper diet.

A year later, though, he developed hearing loss and was sent to another doctor. Soon after, he started having vision problems as well. But tests at the time, including brain scans and standard eye exams, didn’t reveal any underlying physical causes. Over the next two years, his vision continued to worsen, and by the time he saw an eye specialist, he was diagnosed with damage to his optic nerves.

Again, tests looking for a possible explanation like a hereditary disease came up short—but a more sensitive test found that he was still low in vitamin B12. And when they asked about his diet, he revealed that since he was a kid in grade school, he had flat out avoided foods with “certain textures” and almost exclusively ate chips, white bread, processed ham and sausage; he had also stopped taking vitamin B12 shots. Further tests showed that he was deficient in copper, selenium, and vitamin D too, and his bones were unusually weak with low mineral density.

The low vitamin D likely caused the weak bones, but the other deficiencies, the authors wrote, “likely contributed to the patient’s vision and hearing loss.”

Malnutrition to the point of blindness isn’t unheard of, even today, but cases are incredibly rare in developed countries. The boy’s earlier treatment for his B12 deficiency, coupled with some tests that showed his levels were low to normal, had likely delayed the right diagnosis. While the standard test for B12 deficiency is generally reliable, its readings can be affected by antibodies commonly found in people with anemia, which the boy also had.

Plenty of people might call themselves picky eaters, but the boy’s eating habits were so extreme and harmful that doctors felt he met the criteria for avoidant-restrictive food intake disorder, a recently included diagnosis in the Diagnostic and Statistical Manual of Mental Disorders, or DSM. While some people with avoidant-restrictive food intake disorder can experience drastic symptoms like weight loss, many have normal BMI, making it hard to diagnose early.

In addition to getting supplements to treat his nutritional deficiencies, the boy was also referred to mental health counseling for his eating disorder. But sadly, though his vision loss stopped getting worse, his eyesight didn’t improve.

Though the now 19-year-old boy’s prognosis is left unclear in the report, his mother provided an update on his health two years later. She told the Telegraph that he continues to struggle with vision and hearing loss, and that attempts to balance out his diet with supplements and counseling have largely been unsuccessful. “He has no social life to speak of now. After leaving school, he got into college to do a course in IT. But he had to give it up because he could not see or hear anything,” the boy’s mother said.

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