Sunflower cataract occur due to chalcosis. Chalcosis of the lens develop with the presence of copper containing intra ocular foreign bodies or as a pa of Wilson's disease. In this condition copper also gets deposited in basements membrane resulting in Kayser Fleischer ring. Retention of iron containing foreign bodies can cause cataract due to toxicity from ferrous ions. Deposits within the lens epithelium, iris pigment epithelium and and retinal pigment leads to siderosis. The ferrous ions cause a flower shaped coical fiber opacity, brown pigment deposition on the lens capsule and iris heterochromia. Ref: Clinical Guide to Comprehensive Ophthalmology edited by David A. Lee, Eve J. Higginbotham page 315.