Ocular Siderosis Facts

Ocular siderosis is a sight-threatening, largely preventable complication of a retained iron-containing intraocular foreign body (IOFB) — timely localization and removal is the single most important determinant of visual outcome.

Mechanism

Iron from a retained ferrous IOFB dissociates and deposits in intraocular tissues, catalyzing free radical formation (via the Fenton reaction) that damages epithelial and neural structures throughout the eye — the lens, iris, ciliary body, and critically, the retina and RPE.

Clinical signs

• Heterochromia — the affected iris often becomes rusty/brown
• Anterior subcapsular cataract with a characteristic rust-colored discoloration
• Pupillary mydriasis with poor light reaction (iris sphincter toxicity)
• Secondary open-angle glaucoma from trabecular meshwork iron deposition
• Retinal pigmentary changes and progressive RPE degeneration
• Progressive, often painless vision loss over months to years if the foreign body goes undetected

Diagnosis

• History of penetrating trauma is the key alert — always maintain a high index of suspicion after any projectile or metal-on-metal injury, even with a seemingly minor entry wound
• Orbital CT is the imaging investigation of choice for localizing a suspected metallic IOFB (avoid MRI if a ferromagnetic foreign body is suspected)
• Electroretinography (ERG) is the key functional test — a progressively reduced b-wave amplitude reflects ongoing toxic retinal damage and can help gauge urgency and monitor recovery after removal

Management

• Prompt surgical removal of the IOFB is the definitive treatment — via pars plana vitrectomy for posterior segment foreign bodies, or magnetic extraction where accessible and appropriate
• Earlier removal is directly associated with better visual and electroretinographic outcomes — this is not a "watch and wait" condition once siderosis is suspected
• Associated complications (cataract, glaucoma) are managed on their own merits once the foreign body is addressed — cataract surgery may be needed once siderosis-related lens changes progress
• ERG can show partial recovery of retinal function after timely IOFB removal, reinforcing the value of early intervention even when some damage has already occurred

Key reference: Kannan NB, et al. Management of Ocular Siderosis: Visual Outcome and Electroretinographic Changes. J Ophthalmol. 2016.