In this study the alterations of the pattern of the fatty acids of the retinal phosphatides after intravitreal injection of ferrous ammonium sulphate are treated. In vitro and in vivo a significant decrease of the highly unsaturated fatty acids of the C22 type occurs. This lesion spreads from the region of direct contact between iron and retina towards the periphery within 24 hs. The reliability of the experiment is ensured by the proof of analogous changes in human globes affected with siderosis. Finally, the production of lipid peroxides as a cause of the breakdown of the retinal function is discussed.