This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
The most common mode of spread of retinoblastoma: 
Select and explain. 
A. Optic nerve invasion, B. Lymphatics, C. Vascular, D. Direct invasion
A: Optic nerve invasion
Answer: A: Optic nerve invasion 
Explanation: Ans: A. Optic nerve invasion(Ref Kanski 7/e p510-517; Yanoff and Duker 4/e p793)Most common mode of retinoblastoma spread-By optic nerve invasion.Direct extension by continuity to optic nerve & brain seen.Retinoblastoma:Primary malignant intraocular neoplasm.Arising from immature retinoblasts within developing retina.Most common primary intraocular malignancy of childhood in all-racial groups.Strong tendencies invading brain optic nerve & metastasize widely.