Retinoblastoma occurs most often in children younger than five and affects boys and girls in equal numbers. The tumor may be in one eye (referred to as unilateral retinoblastoma), or in both eyes (bilateral retinoblastoma).Retinoblastoma tumors start in the retina, the light-sensitive layer of the eye that lets people see. About 75 percent of retinoblastoma cases are in one eye only, and 90 percent of retinoblastoma patients have no family history of the disease.
Most children with retinoblastoma in the United States — more than 95 percent — survive the cancer and have normal lives. In addition, more than 90 percent of patients keep at least one eye, and most children maintain normal vision.
The cornea is the clear portion of the front of the eye. The conjunctiva is a tissue which lines the eyelids and the eyeball up to the edge of the cornea. The iris is the colored portion of the eye. It is made up of a spongy tissue and is an extension of the choroid. The pupil is the opening in the iris which allows light into the eye. The lens helps focus light rays onto the retina. The lens can change shape, or “accommodate,” to focus on near or distant objects.
The eye is filled with fluids which help nourish and maintain the pressure within the eye. The anterior chamber, the front portion of the eye between the iris and the cornea, is filled with aqueous humor, a watery fluid, which nourishes the lens and maintains the pressure within the eye. The back portion of the eye is filled with vitreous humor, a transparent gel. The retina is made up of ten layers and contains millions of cells. The optic nerve has nerve fibers which transmit information to the brain for interpretation of objects seen and contains about a million cells.
The macula is the area of the retina that is responsible for central vision. Its central portion is referred to as the fovea and is responsible for the sharpest vision. The macula houses the highest concentration of the cones which are responsible for color and sharp vision. The rest of the retina is composed of rods, which are more sensitive to light and are responsible for night vision and peripheral vision.
Attached to the outside of the wall of the eye are six muscles that aid in the movement of the eye. Movement of the eye is caused by shortening of the eye muscles
Most retinoblastoma patients have a white pupil reflex, or leukocoria, instead of a normal black pupil or red reflex. This is sometimes called cat’s eye reflex. Many times the parent is the first one to notice the cat’s eye reflex. This condition may be a sign of another disorder and does not always mean a child has retinoblastoma. An ophthalmologist can make the correct diagnosis.
A crossed eye, or strabismus, is the second most common symptom of retinoblastoma. The child’s eye may turn toward the ear or toward the nose.
Children with retinoblastoma may also have the following symptoms:
- a painful, red eye
- poor vision
- inflammation of tissue surrounding the eye
- an enlarged or dilated pupil
- different colored irises (a condition known as heterochromia)
- failure to thrive (trouble eating or drinking)
- extra fingers or toes (a condition known as hexadactylism)
- malformed ears
- delayed development or retardation