There was a sad story in the news today about a teenager who went blind due to living on a diet of junkfood - chips, crisps, bread, and no fruit or vegetables.
Even the BBC article, linked to in the previous sentence, takes this opportunity to 'lecture' on how vegans can get vitamin B12, although the problem in this case was clearly nothing to do with a vegan diet (it mentions that he had occasional ham or sauage).
This piece at The Conversation goes even further, with the gratuitous statement that "Without nutrient supplements or fortified foods, strict veganism can lead to irreversible blindness." This is true, but the case supposedly under discussion shows that a non-vegan diet can also lead to irreversible blindness, if lacking essential nutrients.
The case in question involves a 'picky eater' who may even qualify as having an eating disorder, but the more important general lessons are probably those about nutritional education and the dangers of food poverty.