Amy Williams of RNZ

A parent of a teenager who eats only plain foods including bread, crackers and pasta says it is terrifying to learn such restrictive diets can cause permanent vision loss.

It follows two eye specialists' warning there were children in New Zealand who had gone blind due to malnutrition.

Sarah and her husband have tried everything to get their son, whose eyesight is good, to eat a balanced diet.

"He is a very plain beige food eater and he's been like that from a very young age."

She said her son will eat only plain foods such as bread, crackers, chips, pasta and brown rice.

"It's really hard.…