It's a rare, but very aggressive form of cancer that affects around 50 children a year in this country.
Four-year-old Gracie Hyland from Northampton was diagnosed with the disease after a family friend saw her photo on Facebook and realised something was not quite right.
Now Gracie and her family have gone back online with a film about their story for CHECT, the charity which helps families affected by Retinoblastoma.
The majority of children are diagnosed with retinoblastoma between birth and five years old. One child is given the diagnosis every week in the UK. 98% survive the condition.
Three quarters - like Gracie - have their eye removed and are fitted with a prosthetic eye. Worn like a contact lens.
"You know she put herself in quite a tricky situation because at a time when people were giving us loads of congratulations she said I've seen Gracie's picture and I've seen a little white glow in her eye and I've heard that can be quite serious."
Doctors confirmed it was retinoblastoma...
"They have an amazing club called the eye club. And the older, more experienced children show the younger children how to take their eye out, how to care for it, how to clean it. A four-year-old looking up to an 8 year old girl thinks wow if she can do it I can do it."
But there is one problem with having a special eye. Gracie's little sister. She wants one too...
Retinoblastoma (Rb) is a rare form of cancer which affects the retina of children predominantly under the age of six years.
Statistically it affects 1:20,000 live births each year. This can also be expressed as 50 cases a year or about one child a week in the UK. It represents 3% of childhood cancers in the UK.
The signs of retinoblastoma include (a) the appearance of a whitish light bouncing back out of the eye, like a 'cat's eye' caught in the light. It is often noticed in photographs where flash photography has been used. One eye will appear red, the other white.
There can be other reasons why this reflex occurs but it is always best to get it checked out (b) a squint is sometimes present (c) the eye can look sore or swollen (d) there can be a change in colour of the iris (e) a deterioration in vision, or (f) the absence of red eye in a photograph in one pupil.