Corneal 'rust ring' If the foreign body is made of iron then there may be a residual 'rust ring' on the cornea after it has been removed. This should be left on for about 2 days for it to soften and then removed by an Ophthalmologist. These 'rust rings' usually cause a corneal abrasion which should be managed appropriately. Author Egyptian Doctor used site: http://www.fastbleep.com/biology-notes/20/48/298 The explanation given by the author Egyptian Doctor is too weak to be educational. Thumb down.