https://www.newscientist.com/article/2218476-app-can-detect-signs-of-eye-diseases-in-kids-by-scanning-your-photos/#ixzz63s2EaCuR

Camera flashes often can make people’s pupils look red in photos. More rarely, flashes can make them appear white – which is usually just a trick of the light but can be a sign of disease, including an eye cancer most common in young children.