Although different types of eye cancer require different diagnostic tests, diagnosis of all eye cancers typically begins with an eye examination by an ophthalmologist (a physician who specializes in diseases that affect the eye). An ophthalmologist examining an eye for melanoma will look for enlarged blood vessels around the eye, which can indicate the presence of a tumor (an abnormal mass of tissue) inside the eye. The ophthalmologist will also view the eye with a special instrument called an ophthalmoscope, which allows the detection of a tumor or other abnormality. However, other tests are needed to confirm a diagnosis. These may include:

• Ultrasound. A test that uses high-frequency sound waves to echo off a tumor and create a pattern. Because melanomas have a specific appearance on ultrasound, this test is often heralded as the best test for diagnosing melanomas of the eye prior to surgery. In fact, ultrasound allows physicians to confirm a diagnosis of eye melanoma in more than 80 percent of cases.
  
  
• Fluorescein Angiography. A procedure in which fluorescent dye is injected into the bloodstream and images of the back of the eye are captured using a special light that causes the dye to glow. Angiography may allow the physician to identify and rule out other eye conditions although it is not particularly useful in diagnosing eye melanomas.

Although biopsies are recommended for confirming most cancer diagnoses, they are not generally used to diagnose eye cancers. During a biopsy, a tiny needle is passed into the eye, and tumor cells are collected through a small syringe. Eye biopsies are difficult to perform and the risk of damaging the eye or inadvertently spreading the tumor outside the eye is too great.

If intraocular melanoma is found, the physician may order the following tests to determine if the cancer has spread (metastasized) to other areas of the body:

• Chest x-ray. Sometimes the physician will order a chest x-ray to see if the cancer has spread to the lungs. This is highly unlikely unless the cancer has reached an advanced stage.
  
  
• CAT (computed axial tomography) scan. This x-ray procedure produces numerous cross–sectional images of the body to help determine if cancer has spread to distant sites. CAT scans take longer than x-rays and require the patient to lie still on a table for the duration of the procedure. Before a CT scan, patients will often be injected with a radiocontrast agent, or dye, which outlines the structures in the body more clearly.

• MRI (magnetic resonance imaging). This procedure uses strong magnets and radio waves to produce cross-sectional images of the body, much like a CAT scan. In addition, MRIs can also produce images that are parallel with the length of the body, which can be useful in identifying the spread of cancer. MRI requires the patient to lie inside a tube-like structure, and a contrast material or dye may or may not be administered intravenously in the arm.

During an eye examination for intraocular lymphoma, the ophthalmologist will look for cloudiness in the vitreous, the gel that fills the interior of the eye. If this cloudiness does not dissipate with treatments commonly prescribed for the inflammation called uveitis (a noncancerous problem), the ophthalmologist may order an ultrasound, MRI or (rarely) CAT scan. The following tests may also be ordered:

• Vitrectomy.  A type of biopsy in which a needle-like instrument is used to remove a sample of the vitreous fluid or a piece of the tumor is removed through a small incision and examined.
  
  
• Spinal tap (also called lumbar puncture). A needle is inserted into the lower back to obtain a small sample of the fluid that surrounds and protects the brain and spinal cord (cerebrospinal fluid). The cerebrospinal fluid is then examined for lymphoma cells under a microscope because lymphoma of the eye can spread to the brain.

A retinoblastoma examination will include a detailed family history because approximately 40 percent of these cancers are inherited. If a parent is known to have the genetic defect, a specialized blood test can identify the gene in an infant in the first months of life. Infants at risk for retinoblastoma will have regular eye exams during infancy.

During the exam, the ophthalmologist will view the retina with special instruments and magnifying lenses. The child may be put to sleep with general anesthesia so the ophthalmologist can examine the affected eye(s) more carefully. Imaging tests such as ultrasound, CT scans and MRIs can also be used to diagnose retinoblastoma. Children may be sedated for these tests when they require the patient to remain still for an extended period of time.

In addition, the oncologist may occasionally order radionuclide imaging, which shows whether the cancer has invaded the skull and other bones. During this procedure, radioactive dye injected into the patient accumulates in any diseased bones in the skeleton.  These areas of diseased bone appear dense and gray on the bone scan, indicating possible areas of metastasis. Physicians may then order additional tests to determine if the areas are secondary cancers or other conditions.