The youngster’s family, from Bristol, realised something was seriously wrong when he began to lose his hearing at the age of 14.
His eyesight also quickly deteriorated and he has now been left with no job and no social life as a result, his mother says.
The woman, who asked not to be named, said her son began going off his meals when he was about seven years old and would only eat chips, Pringles, sausages, processed ham and white bread.
She said: “The first we knew about it was when he began coming home from primary school with his packed lunch untouched.
“I would make him nice sandwiches and put an apple or other fruit in and he wouldn’t eat any of it. His teachers became concerned too.
“His brother and sister have never stopped eating. They love everything. But he was just as fit and healthy as them.
“He has always been skinny so we had no weight concerns. You hear about junk food and obesity all the time – but he was as thin as a rake.”
The teen, now 19, suffers from an eating disorder known as ARFID (avoidant-restrictive food intake disorder).
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Those suffering from the condition often avoid food with a certain texture, smell, taste or appearance, or only eat it at a certain temperature, according to eating disorder charity Beat.
The teenager’s lack of nutrition severely damaged his optic nerve, causing a condition known as nutritional optic neuropathy (NON).
His mother, who is in her 40s, said: “We couldn’t believe it when we were told what had happened.
“His sight went downhill very fast – to the point where he is now legally blind.
“We are told the damage is irreversible; it’s been a nightmare.
“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.”
Dr Denize Atan, who has been caring for the teenager, said the unnamed patient is still eating mostly the same food – although his nutrition has improved through vitamin supplements.
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Dr Atan, of University Hospitals Bristol NHS Foundation Trust, added: “When this behaviour starts as a child it tends to continue as an adult.
“The processed food was not the problem per se. It was he was only eating that type of food and nothing else.
“Nutrients are extremely important for vision and hearing – but a lot of people are not aware of that.”
The family agreed for the case to be reported in the journal Annals of Internal Medicine to raise awareness of ARFID and the importance of nutrition for good eye and ear health.
SWNS contributed to this report.