Retinoblastoma is a malignant tumor (cancer) of the retina (part of the eye) that generally affects children under the age of 6.

Retinoblastoma occurs when a cell of the growing retina develops a mutation in the RB gene (a tumor-suppressor gene). This mutation causes the cell to grow out of control and become cancerous.

Sometimes this mutation develops in a child whose family has never had eye cancer, but other times the mutation is present in several family members. If the mutation runs in the family, there is a 50% chance that an affected person's children will also have the mutation. They will therefor have a high risk of developing retinoblastoma themselves.

One or both eyes may be affected. A visible whiteness in the pupil may be present. Blindness can occur in the affected eye, and the eyes may appear crossed. The tumor can spread to the eye socket, and to the brain, through the optic nerve. This is a rare tumor, except in families that carry the RB gene mutation.

• A white glow in the eye that is often seen in photographs taken with a flash; instead of the typical "red eye" from the flash, the pupil may appear white or distorted.
• White spots in the pupil
• Crossed eyes
• A red, painful eye
• Poor vision
• The iris may be a different color in each eye.

• An examination of the eye with dilation of the pupil
• A CT or MRI study of the head to evaluate tumor and possible spread
• An ultrasound of the eye (head and eye echoencephalogram)