You might have heard of this trick before, but take note — it’s literally a lifesaver. Retinoblastoma is a rare type of aggressive eye cancer that almost exclusively affects young children. It develops as a tumor in the retina but can be diagnosed with just a smartphone. Children who have the disease often have a white glow around their pupils that shows up when photographed with a flash — and it's this fact that recently  saved the life of Julie Fitzgerald's two-year-old son, Avery.