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Ultrasound biomicroscopy in two cases of ocular siderosis with secondary glaucoma

Editor, S iderosis bulbi is a disease caused by a retained intraocular ironcontaining foreign body (IOFB). A history of ocular trauma combined with heterochromia, mydriasis, pigmentation of the anterior chamber structures and a reduced electroretinographic response all provide an inkling of the diagnosis (Sneed & Weingeist 1990). Affected eyes can often present with a severe increase in intraocular pressure (IOP) (Talamo et al. 1985). A precise radiological and ⁄or echographic localization of the IOFB, ideally supported by histological analysis of a biological sample, are vital to the confirmation of the disease. This article describes two cases of secondary glaucoma caused by the retention of an IOFB. An ultrasound biomicroscopy (UBM) examination (UBM Model P40; Paradigm Medical Industries Inc. Salt Lake City, UT, USA) was performed in both patients and the findings are discussed below. Patient 1: An 11-year-old boy received a fragment of a bullet in his left eye. The sclera was promptly sutured but a small IOFB was overlooked. Two months later, the injured eye presented traumatic cataract with uveitis. On gonioscopy, the irido-corneal angle showed conspicuous rustbrown pigmentation in the trabecular meshwork (TM) and the IOP was 30 mmHg on average. Computed tomography showed the presence of a piece of iron in the nasal ora serrata (about 2 mm in length), which was removed surgically via pars-plana vitrectomy with polydimethylsiloxane (PDMS) tamponade and phacoemulsification of the lens. PDMS was removed uneventfully after 1 month. However, after one more month, trabeculectomy with mytomycine-C application was necessary to achieve satisfactory control over IOP. The preoperative UBM showed an unusually high reflectivity in the deep angular stroma compared to the regular echographic pattern of the fellow eye (Fig. 1A–D). Histological examination of a TM sample, taken during a subsequent surgical revision of the filtering bleb, confirmed the diagnosis of ocular siderosis. Patient 2: A 27-year-old man suffered an injury to his left eye while he was hammering metal. The IOFB, initially misdiagnosed, was found in the superior ora serrata during a parsplana vitrectomy with phacoemulsification of the lens performed 3 months after the trauma. On gonioscopy, the TM pigmentation was much more brown and dense than in the right (healthy) eye. After four more months, filtering surgery became necessary to control the IOP increase. The histological evaluation of a sample of iris and TM was positive for iron staining and showed alterations compatible with siderosis bulbi. The preoperative UBM findings were remarkably similar to those obtained in the patient described previously. The aetiopathogenesis of secondary open-angle glaucoma related to ocular siderosis has often been ascribed to trabecular fibrosclerosis, probably because of the direct toxic effect of iron ions (Appel & Barishak 1978). In the first presented case, severe glaucoma developed 2 months after the trauma with the metal foreign body still in the eye. In the second case it appeared approximately 7 months later, with an initial 3-month retention of the IOFB. IOP elevation did not resolve in either patient after IOFB removal.