<prompt> Gene for retinoblastoma is found on which chromosome13141516  <response>: A 13 300- Khurana 5th Retinoblastoma appears to result from loss or inactivation of both normal alleles of the retinoblastoma gene a DNA sequence located on long arm chromosome 13, the q 14 region It is the most common primary intraocular malignancy of childhood Remember MC orbital malignancy of childhood is Rhabdomyosarcoma Knudsons proposed two- hit hypothesis of oncogenesis for Retinoblastoma Retinoblastoma Heritable germineNon Heritable somatic 40 tumours Bilateral multifocal tumours Predisposition ot second non ocular cancersPineloblastoma osteosarcoma 60 tumours Unilateral Presence of leukoria white pupillary reflex and calcification within the globe in a one and half year old child is almost diagnostic of retinoblastoma Most common presentation of Retinoblastoma is leukocorea or amauratic cat s eye reflex and strabismus Other presentationsi Secondary glaucomaii Red eyeiii Buphthalmos proptosisiv Orbital cellulitisv Painful red eye usually associated with pseudohypopyon and hyphaema picture stimulating iridocyclitisvi Excessive tearingvii Corneal clouding due to elevated IOPviii Discolouration of iris due to neovascularization of iris LDH Is grossly increased in Retinoblastoma where the aqueous plasma ratio of LDH is greater than 1.5 Ultrasound CT scan are able to detect a intraocular mass with calcification, which is pathognomic of retinoblastoma. MRI is not able to detect the calcification as wall as CT but it is investigation of choice to study the optic nerve sellar and parasellar regions of the brain. The most common method of spread of retinoblastoma is by direct invasion of optic nerve with extension in to theCNS, Hematogenous spread may lead to distant metastasis throughout the body. Rosettes are characteristic in retinoblastoma 