Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, the light-detecting tissue of the eye. It is the most common primary malignant intraocular cancer in children, and 80% of retinoblastoma cases are first detected in those under 3 years old.

Though most children in high income countries survive this cancer, they may lose their vision in the affected eye(s) or need to have the eye removed.

Almost half of children with retinoblastoma have a hereditary genetic defect associated with it. In other cases, retinoblastoma is caused by a congenital mutation in the chromosome 13 gene 13q14 (retinoblastoma protein).

Retinoblastoma is the most intrusive intraocular cancer among children. The chance of survival and preservation of the eye depends fully on the severity. Retinoblastoma is extremely rare as there are only about 200 to 300 cases every year in the United States. Globally, only 1 in about 15,000 children have this malignancy, though rates continue to increase.

Intraocular malignancies are relatively more frequently treated than extraocular malignancies, likely due to a relatively earlier detection and subsequent treatment. Pediatricians may screen infants with annual vision tests, in which anomalies can be detected. During a red reflex test, light from an ophthalmoscope goes through transparent parts of the eye and reflects off the ocular fundus. If retinoblastoma is present, it may partially or fully impede light transversing this path. This may result in an abnormal red reflex or leucocoria, which can be a common indicator of retinoblastoma (when light is reflected by the tumor, the regular view of the red retina is blocked). The retinoblastoma may be visible as a whitish, translucent mass. If the tumor has not spread and is contained within the eye, chances of successful treatment are favorable. If initial signs are ignored or diagnosis is significantly delayed, outcomes and prognosis worsen. The effects of retinoblastoma may spread outside the eye, sometimes resulting in proptosis. Retinoblastoma that has spread may be significantly more difficult to treat.

The most common and obvious sign of retinoblastoma is an abnormal appearance of the retina as viewed through the pupil, the medical term for which is leukocoria, also known as amaurotic cat's eye reflex. Other signs and symptoms include deterioration of vision, a red and irritated eye with glaucoma, and faltering growth or delayed development. Some children with retinoblastoma can develop a squint, commonly referred to as "cross-eyed" or "wall-eyed" (strabismus). Retinoblastoma presents with advanced disease in developing countries and eye enlargement is a common finding.

Depending on the position of the tumors, they may be visible during a simple eye examination using an ophthalmoscope to look through the pupil. A positive diagnosis is usually made only with an examination under anesthetic (EUA). A white eye reflection is not always a positive indication of retinoblastoma and can be caused by light being reflected badly or by other conditions such as Coats' disease.

The presence of the photographic fault red eye in only one eye and not in the other may be a sign of retinoblastoma. A clearer sign is "white eye" or "cat's eye" (leukocoria).