When there is difficulty adjusting to darkness or night blindness. A severe or prolonged deficiency of vitamin A causes changes in the cells of the lining of the cornea, which eventually lead to corneal ulcers and blindness.
Treatment: With vitamin A supplements, the number of supplements will depend on the age of the child. They can reverse night blindness and can also help re-lubricate the eyes. But the loss of vision caused by corneal ulcer healing is irreversible, prevention is through a balanced diet and vitamin supplements.