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
Which among the following is the most toxic intraocular foreign body? 
Select and explain. 
A. Glass, B. Iron, C. Lead, D. Copper
B: Iron
Answer: B: Iron 
Explanation: Intraocular foreign body of iron causes maximum damage to the eye. Siderosis bulbi refers to the degenerative changes produced by an iron foreign body retained inside the eyeball. The iron paicles undergo electrolytic dissociation. The iron ions combine with the intracellular proteins and produce degenerative changes. Epithelial structures are most affected. Ref: Comprehensive Ophthalmology by AK Khurana, 3rd edition, Page 494.