(CNN) - Eating a diet of french fries, Pringles and white bread was enough to make one teenage boy lose his sight, according to a case study published in a medical journal.

Scientists from the University of Bristol examined the case of a young patient whose extremely picky eating led to blindness, and have warned of the dangers of a poor diet.

The unidentified patient told doctors he had only eaten fries from the fish and chip shop, Pringles potato chips, white bread, slices of processed ham and sausage since elementary school, and he avoided foods with certain textures. He first visited a doctor at age 14, complaining of tiredness, according to a case report published in the Annals of Internal Medicine on Monday.

He wasn't taking any medication, had a normal BMI and height, and showed no visible signs of malnutrition.

Doctors discovered low vitamin B12 levels and anemia, treating the patient with vitamin B12 injections and offering dietary advice.

One year later there were signs of hearing loss and vision symptoms, but doctors did not find the cause.

His vision had worsened to the point of blindness by 17 years of age, and doctors identified vitamin B12 deficiency, low copper and selenium levels, a high zinc level, reduced vitamin D level and bone level density, according to a statement from the University of Bristol.

By this stage, vision damage was permanent.

Researchers from Bristol Medical School and the Bristol Eye Hospital examined the case and concluded that the patient suffered nutritional optic neuropathy, a dysfunction of the optic nerve.

In developed countries it is mostly caused by bowel problems or medication that interferes with the absorption of nutrients, and it is rarely caused entirely by poor diet because food is readily available.

In some places, malnutrition caused by poverty, war and drought is linked to higher rates of nutritional optic neuropathy, according to a statement.

The condition is reversible if treated early but can lead to blindness if no action is taken.

"Our vision has such an impact on quality of life, education, employment, social interactions, and mental health," said study lead author Denize Atan, an ophthalmologist at Bristol Medical School and Bristol Eye Hospital.

"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."

The researchers say that poor diet and reduced intake of minerals caused vision loss in this case, and warn that nutritional optic neuropathy could become more common due to the consumption of junk food.

They also warned vegans to make sure to supplement for vitamin B12 to avoid deficiency.

To prevent similar cases, doctors should ask patients about their dietary history as part of routine clinical examinations, the researchers urged.

Extreme example

Tom Sanders, a professor of nutrition and dietetics at King's College London, was critical of the case report, saying it relied on the patient's own recall of his eating habits and did not take into account other possible explanations for the condition, including genetic defects or environmental exposures.

"Vitamin B12 deficiency can cause optic neuropathy but it is very unusual to find dietary deficiency when animal products are consumed e.g. ham and sausages which are significant sources of the vitamin B12," he told the Science Media Centre in London.

Gary Frost, a professor of nutrition and dietetics at Imperial College London, who was not involved in the research, told CNN it is incredibly rare for someone in the UK to have a diet so limited it results in micronutrient deficiencies.

"Although it is an extreme example, it highlights the importance of having a wide and varied diet to ensure that you get the profile of nutrients and micronutrients that are needed for healthy development," said Frost.

These deficiencies become more likely the more limited the choice of food, he added.

"Fussy eating is very common in young children and in extreme cases can lead to very limited choice of food," said Frost.

"There is a need to pick up on eating problems such as these as early as possible so the issue around limited textures and tastes can be addressed."