Retinoblastoma is an aggressive, deadly eye cancer that mainly affects young children.
It grows quickly, but if it's detected early it can save the child’s life and possibly prevent the removal of the eye.
A new campaign by the Childhood Eye Cancer Trust is demonstrating how to detect the disease using just a smartphone camera.
The campaign illustrates the test using a series of interactive posters that show a close up of a child’s eye with a normal-looking pupil.
When you take a photo of a child with Retinoblastoma, the pupil can sometimes appear white
When you take a photo of the poster using the flash, reflective particles embedded in ink printed on the pupil mean that it appears bright white instead of black.
A white mark like this on a child’s eye when you use a flash to take a photo - like a cat’s eye reflecting light - is one indicator of an eye tumour.
As the name suggests, the cancer affects the retina at the back of the eyeball. If the tumour is not treated, the cancer cells grow and fill up the eyeball, leading to loss of vision and potentially spreading to the brain, bones and lymph nodes.
If the cancer spreads to any of these other places it can be very difficult to treat.
If caught early, small tumours can be treated with laser therapy, while larger ones may need chemotherapy, radiotherapy or surgery.