Retinoblastoma is a rare cancer that occurs in the eyes of young children. Tumors appear on the retina, the "movie screen" that covers the rear inside wall of the eyes. These tumors can make a child's pupil look white instead of black.

In the United States and northern Europe, retinoblastoma occurs once in every 15,000 to 16,000 births. About a quarter of the cases are hereditary and have been linked to a specific gene mutation. The cancer can occur in one or both eyes.

Fatal if left untreated, the tumors can spread to the brain via the optic nerve. Treatment for retinoblastoma can include chemotherapy, radiation and surgery. In some cases, the eye must be removed. The overall five-year survival rate for children with retinoblastoma in the United States is 93 percent.

A retinoblastoma tumor can usually be seen with a flashlight. It may first be noticed in flash photographs. Instead of the usual "red eye," the child's pupil will look white.

Retinoblastoma may also cause lazy eye (strabismus), a condition in which the eyes don't appear to look in the same direction.

Less common signs and symptoms include:

• Vision problems
• Eye pain
• Redness of the white part of the eye
• A pupil that doesn't contract when exposed to bright light

Each cell in the body carries the same set of genes. Retinoblastoma is caused by a mutation in one of these genes. In about 60 percent of the cases, this gene mutation occurs in a single cell in the eye, so only that eye develops a tumor. These sporadic mutations may be random errors that occur during normal cell division.

In the remaining 40 percent of cases, the gene mutation occurs in every cell of the body. This form of retinoblastoma is called hereditary, because it can be passed on to future generations. Oddly enough, only 25 percent of children with hereditary retinoblastoma inherit it from their parents. The others develop the mutation in all their cells after conception, while they're in the womb.

If either parent had the hereditary form of retinoblastoma, their child would have a 50 percent chance of inheriting the mutated gene that causes the disorder. Doctors recommend that these children receive eye exams every few months until the age of 3. A blood test can determine if the child has inherited the gene for retinoblastoma.

With the hereditary form of the disease, having retinoblastoma in one eye increases the risk of developing it in the other eye. Most children with hereditary retinoblastoma get tumors in both eyes at the same time. In some cases, however, one eye will develop retinoblastoma a year or more before the other eye.

Neither race nor sex seems to be a factor in developing retinoblastoma.

If you notice something odd about your child's eyes, especially if the pupil looks white instead of black, make an appointment to see your family doctor or pediatrician. More treatment options are available when retinoblastoma is diagnosed early. You may be referred to an eye specialist (ophthalmologist) who works primarily with children.

The ophthalmologist will need to look very carefully inside your child's eyes. Because small children have a hard time submitting to such an exam, your child may be given anesthesia so he or she will sleep through the procedure.

In most cases, the specialist can identify retinoblastoma just by looking at it with special lights and magnifying lenses. Imaging tests can help determine how large the cancer is and if it has spread. These tests include:

• Ultrasound. If the tumor is so large that the doctor can't see the entire interior of the eye, ultrasound may be used, because of its ability to see through tissue.
• Computerized tomography (CT). To highlight details on the CT scan, a harmless dye may be injected before the X-rays are taken. CT scans often are used for rapid assessment of abnormalities.
• Magnetic resonance imaging (MRI). An MRI can show more detail than a CT scan, but an MRI takes longer to perform. Because it is difficult for young children to hold still, your child may have to be sedated for an MRI.

Children who have the hereditary form of retinoblastoma are at higher risk their entire lives for developing other types of cancers. The most common types are:

• Osteosarcoma — a variety of bone cancer
• Soft tissue sarcomas — cancers that develop in muscles, tendons, ligaments and fatty tissue
• Malignant melanoma — a very aggressive form of skin cancer

Less common cancer risks include brain tumors, lung cancer, lymphoma and breast cancer. Regular screenings can help catch these cancers at an early stage.

The type of treatment chosen depends on many factors, including the size of the tumor and whether one or both eyes are affected. According to the American Cancer Society, more than 90 percent of children with retinoblastoma can be cured. The odds are even better for children whose tumors haven't spread outside the eyeball.

If retinoblastoma affects just one eye, the tumor often grows so large that it permanently destroys vision in that eye. In these cases, the most common procedure is to remove the eye. An artificial eye can be fashioned to match the child's remaining eye.

When retinoblastoma affects both eyes, doctors may use a variety of treatments in an effort to preserve as much vision as possible. They include:

• External radiation. Beams from a radiation machine are focused on the retina. Treatments are typically given five days a week for three or four weeks. Each treatment takes just a few minutes. One of the risks of this type of therapy is that it can inhibit the growth of bone and other tissues near the eye. It also may make your child more likely to develop other types of cancers.
• Internal radiation. Radioactive material is temporarily placed inside the eye socket, next to the eyeball. Your child is asleep during the operations to insert and remove the radioactive material — which is left in the eye socket for four or five days. This procedure is used only with small tumors.
• Lasers. Cancer cells are destroyed by heat caused by laser beams, which are shot through the eye's pupil. Your child is asleep for this treatment, which is usually repeated once a month for up to three months. It's effective only for small tumors.
• Freezing (cryotherapy). A probe is cooled to very low temperatures and then placed on the outside of the eyeball, next to the tumor. The eye and eyelid might be swollen for a few days. Your child is asleep for this procedure, which must be repeated several times to be successful and is useful only for small tumors.
• Chemotherapy. Some cancer drugs are taken by mouth, while others are injected into a vein. Either way, they affect the entire body, which is helpful in fighting cancers that have spread. Retinoblastomas tend to become resistant to chemotherapy, so different combinations of drugs may be tried.

There is no way to prevent retinoblastoma, but families affected by the disorder may want to consider genetic testing. For example, if your child has retinoblastoma, you may want to test his or her siblings — especially younger ones. If they have the mutated gene, you can increase the frequency of screenings for the disorder. Treatment is most effective when the disorder is found in early stages.

Genetic testing also can determine if your child has the type of retinoblastoma that can be passed down to his or her children. This information will help your child make family planning decisions in the future.