Ocular siderosis caused by a subretinal iron foreign body masquerading as a blood clot: a case report

Purpose: We report a case of ocular siderosis caused by a subretinal iron foreign body. Observations: A 30-year-old male construction worker injured by a small piece of shrapnel while working visited an eye clinic for decreased vision in left eye on day X, and was subsequently referred to our hospital with a diagnosis of vitreous hemorrhage on day X+1. Although a penetrating foreign body was suspected, no obvious wound or intraocular foreign body was found even after the hemorrhage subsided. On X+3 months, a rhegmatogenous retinal detachment was found and a lens-sparing vitrectomy was performed. A black elevated subretinal lesion was noted intraoperatively but not removed because it was considered to be a blood clot. The postoperative course was stable with best corrected visual acuity (BCVA) recovering to 20/16. However, the BCVA decreased to 20/30 on X+11 months with the subretinal lesion turning reddish brown. The electroretinogram also showed a significant attenuation of all stimuli. Siderosis was considered to have developed due to the subretinal foreign body. On X+14 months, we performed a combined phaco-vitrectomy to remove the foreign body. Analysis revealed iron as the main component of the foreign body. However, the postoperative electroretinogram remained unchanged, and the BCVA was 20/63 without improvement. Conclusions and importance: We experienced a case of a subretinal iron foreign body being mistaken for a blood clot. Even if the vision stays stable, ocular siderosis may occur over the long term if a subretinal iron foreign body remains. Therefore, surgical removal should be actively considered when a subretinal iron foreign body is suspected.