>93% RB1 mutation detection sensitivity),  the risk of a germline RB1 mutation is reduced to less than 1%, a level at which only clinic examination (and not examinations under anaesthetic) is recommended for the affected individual and their future offspring (National Retinoblastoma Strategy, Canadian Guidelines for Care). Imaging
Traditional ultrasound B scan can detect calcifications in the tumour while high-frequency ultrasound B scan is able to provide higher resolution than the traditional ultrasound and determine the proximity of the tumour with front portion of the eye. MRI scan can detect high-risk features such as optic nerve invasion; choroidal invasion, scleral invasion, and intracranial invasion. CT scan is generally avoided because radiation can stimulate the formation of more eye tumours in those with RB1 genetic mutation. Staging
In order to properly diagnose retinoblastoma, there must be guidelines to follow to properly classify the risk of the tumor. The Reese Ellsworth Classification System, by Dr. Algernon Reese and Dr. Robert Ellsworth, is universally used to determine the size, location, and multi-focality of the tumor. The system was originally used to decide the best treatment result by using external beam radiotherapy, as well as, the likeliness of salvaging the globe of the eye. Due to chemotherapy not being part of the Reese Ellsworth Classification System, there needed to be an updated classification system to foresee the treatment outcomes of chemotherapy. The International Classification for Intraocular Retinoblastoma is now the current system being used, and it was created by Murphree and associates.
The position, size, and quantity of tumors are considered when choosing the type of treatment for the disease. Differential diagnosis
1. Persistent hyperplastic primary vitreous is a congenital developmental anomaly of the eye resulting from failure of the embryological, primary vitreous, and hyaloid vasculature to regress, whereby the eye is shorter, develops a cataract, and may present with whitening of the pupil. 2. Coats disease is a typically unilateral disease characterised by abnormal development of blood vessels behind the retina, leading to blood vessel abnormalities in the retina and retinal detachment to mimic retinoblastoma. 3. Toxocariasis is a parasitic disease of the eye associated with exposure to infected puppies, which causes a retinal lesion leading to retinal detachment. 4. Retinopathy of prematurity is associated with low-birth-weight infants who receive supplemental oxygen in the period immediately after birth, and it involves damage to the retinal tissue and may lead to retinal detachment.If the eye examination is abnormal, further testing may include imaging studies, such as computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound. CT and MRI can help define the structure abnormalities and reveal any calcium depositions. Ultrasound can help define the height and thickness of the tumor. Bone marrow examination or lumbar puncture may also be done to determine any metastases to bones or the brain. Morphology
Gross and microscopic appearances of retinoblastoma are identical in both hereditary and sporadic types. Macroscopically, viable tumor cells are found near blood vessels, while zones of necrosis are found in relatively avascular areas.