A corneal foreign body causes a non-infectious inflammation of the cornea. It could be contact lens deposits evaluated by the immune system as foreign; antigens cause non-infectious inflammatory responses. Other causes include cellular debris trapped too tightly under the contact lens, toxins from bacteria, or disinfectants.
A foreign body could look like a gray or whitish deposit in the corneal stroma. Larger bodies cause discomfort, pain, photophobia and lacrimation and would manifest itself as an acute red eye syndrome.