Ocular Siderosis

Key points at a glance

Key points of this disease

• Ocular siderosis is a progressive ocular tissue disorder caused by iron ion toxicity due to retained iron-containing intraocular foreign bodies (IOFB).
• The prevalence is rare, about 0.002% of ocular trauma patients, but if overlooked, it can lead to irreversible visual impairment. ¹⁾
• Approximately 96% of patients are male, and the most common mechanism of injury is metal fragment injury during hammer and chisel work. ¹⁾
• Reduction of the b-wave in electroretinography is an indicator of early changes and is important for assessing severity and determining treatment timing. ⁴⁾
• Initial symptoms are often subtle and may be misdiagnosed as chronic anterior uveitis, so attention to missed IOFB is necessary. ³⁾
• Early removal of IOFB improves visual prognosis, and mean BCVA is significantly better compared to the non-removal group. ¹⁾
• Delayed siderotic glaucoma has been reported to develop more than 15 years after injury. ⁴⁾

1. What is Ocular Siderosis?

Ocular siderosis (Siderosis bulbi) is a disease that occurs when an intraocular foreign body (IOFB) containing iron or iron alloy remains in the eye. The retained iron dissolves into the ocular tissues, and iron ions damage various ocular tissues such as the cornea, iris, lens, retina, and trabecular meshwork.

The concept of this disease was first described by Bunge in 1860. Its prevalence is rare, occurring in approximately 0.002% of patients with ocular trauma. ¹⁾ IOFB may remain asymptomatic in the eye initially and gradually cause progressive tissue damage, so delayed diagnosis significantly worsens visual prognosis.

Q Can ocular siderosis occur with metals other than iron?

A

This condition is specific to IOFB derived from iron or iron alloys. Copper-containing IOFB similarly causes severe “ocular chalcosis.” Aluminum, glass, and other materials cause minimal tissue reaction and are distinguished from ocular siderosis.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

Subjective symptoms of ocular siderosis can be divided into those that appear immediately after injury and those that gradually progress after foreign body retention.

• Decreased vision: The most common symptom, occurring in approximately 63.79% of patients. ¹⁾
• Asymptomatic: Symptoms are scarce in the early stage, and about 27.58% of patients are discovered without any subjective symptoms. ¹⁾
• Night blindness and visual field constriction: Appear when selective damage to rod cells progresses.
• Eye pain and redness: Seen in the acute phase of IOFB injury or when inflammation is present.

Clinical Findings

Findings of ocular siderosis reflect the sites of intraocular iron deposition, causing characteristic changes in each ocular tissue.

Cornea

Corneal iron line deposition: Iron deposition in the epithelium or stroma. Observed in approximately 46.55% of patients. ¹⁾

Corneal opacity: In long-standing cases, may progress to stromal opacity.

Iris and Pupil

Siderotic mydriasis (mydriasis siderostica): Characteristic pupillary dilation due to iron-induced damage to the iris sphincter muscle. ³⁾

Iris discoloration: Brownish discoloration of the iris due to iron deposition.

Lens

Siderotic cataract: characteristic brown opacity under the anterior lens capsule. Observed in approximately 37.93% of patients. ¹⁾

Iron deposition on the lens epithelium: As it progresses, opacity spreads throughout the cortex.

Retina

Retinal pigment epithelium (RPE) degeneration: The most frequent finding, observed in approximately 72.41% of patients. ¹⁾

Peripheral retinal degeneration and bone-spicule pigmentation: Seen in long-standing cases.

Complication with glaucoma is also an important finding. In siderotic glaucoma, marked elevation of intraocular pressure (IOP) can occur, with a reported delayed case reaching 58 mmHg. ⁴⁾

Q What is first affected in ocular siderosis?

A

Electroretinographic findings show that rods are selectively affected early. The b-wave amplitude decreases first, and as the condition progresses, the a-wave amplitude decreases, eventually leading to extinction of the electroretinogram. For details, see the “Pathophysiology” section. ⁴⁾

3. Causes and Risk Factors

Causes

The cause of ocular siderosis is the intraocular retention of an IOFB containing iron or iron alloy. Among the mechanisms of injury, hammer and chisel work is the most common, with metal fragments from metalworking and construction work being the most frequent source of injury. ¹⁾

96.49% of patients are male, with a strong association with occupational metal work. ¹⁾

Risk Factors

• Metalworking and construction work: Flying metal fragments from hammering or grinding are the main risk.
• Not wearing protective eyewear: Lack of appropriate eye protection is a major factor in injury. ¹⁾
• Small, high-speed IOFB: These can easily penetrate the eye wall, and the injury may go unnoticed.
• Initially asymptomatic course: Symptoms are mild, leading to delayed consultation and diagnosis.

Prevention and Daily Care

When working with metals (e.g., hammer, grinder, lathe), always wear industrial safety goggles. If you feel a foreign body sensation or vision changes in your eye, even if mild, promptly see an ophthalmologist. Even if you are unaware of an injury, if eye symptoms appear after work, examination considering the possibility of IOFB is necessary.

4. Diagnosis and Examination Methods

Diagnosis of ocular siderosis involves confirming the presence and location of IOFB and assessing iron toxicity to ocular tissues. Since missed IOFB may have unclear trauma history, it is easily misdiagnosed as other diseases. ³⁾

Imaging Tests

CT Scan

Usefulness for metallic IOFB: Thin-slice CT is useful for detecting small intraocular foreign bodies and also helps in locating the foreign body. ²⁾

Prevention of oversight: Even in cases with unclear history, systematic CT search can detect IOFB.

Ultrasound Examination

Non-invasive intraocular evaluation: Highly useful in cases where fundus examination is difficult (e.g., lens opacity, vitreous hemorrhage).

Localization of IOFB: Effective for narrowing down the location, such as the vitreous cavity or subretinal space.

Electroretinography

b-wave attenuation: Captures early changes as an indicator of rod function. Most important for determining treatment timing. ⁴⁾

Severity assessment: Changes in electroretinogram patterns reflect the progression of iron toxicity.

OCT examination

RPE/photoreceptor layer evaluation: Quantitatively assesses the degree of degeneration of the retinal pigment epithelium and photoreceptor outer segments.

Postoperative follow-up: Monitors retinal recovery after IOFB removal.

Caution regarding misdiagnosis

Chronic missed IOFB cases may be misdiagnosed as chronic anterior uveitis. ³⁾ In cases of refractory uveitis or unexplained lens opacity, it is important to take a detailed history of trauma and actively search for IOFB using CT imaging.

Visual Acuity Distribution

Parameswarappa et al. (2023) reported the visual acuity distribution in a cohort of 58 eyes as follows. ¹⁾

Visual acuity at presentation varies widely among patients, ranging from good vision to light perception or worse.

Visual Acuity	Proportion
0.5 or higher (good)	Approximately 34%
0.1 to 0.4 (moderate reduction)	Approximately 29%
Less than 0.1 (severe reduction)	Approximately 37%

Q If CT does not find a foreign body, can ocular siderosis be ruled out?

A

CT sensitivity depends on foreign body size and material. Thin-slice CT is useful for detecting metallic IOFBs, but may fail to detect very small or non-metallic foreign bodies ²⁾. Comprehensive assessment combined with clinical findings (e.g., iron mydriasis, iron rust cataract) is necessary.

5. Standard Treatment

The cornerstone of treatment for ocular siderosis is early removal of IOFB, aiming to halt the progression of iron toxicity.

Surgical IOFB Removal

Vitrectomy (pars plana vitrectomy; PPV) is the main surgical procedure for IOFB removal. ^{1, 2, 3, 4)}

• Use of magnetic probe: Magnetic probes are effective for iron-containing IOFBs and are used in combination with PPV to remove the foreign body from the eye. ³⁾
• Simultaneous cataract surgery: When lens opacity (siderotic cataract) is present, cataract surgery can be performed concurrently with PPV. ²⁾

The distribution of IOFB sites is shown below.

IOFB site	Proportion
Vitreous cavity	Most common
On the retina or under the retina	Second most common
Anterior chamber or lens	Relatively rare

Comparison of visual outcomes

In the report by Parameswarappa et al. (2023), comparing postoperative visual acuity (BCVA) between the IOFB removal group and the non-removal group, the removal group achieved a significantly better visual outcome with a mean logMAR of 1.0, compared to 1.58 in the non-removal group. ¹⁾

Group	Mean BCVA (logMAR)
IOFB removal group	1.0
Non-removal group	1.58

Management of Glaucoma

When siderotic glaucoma develops, intraocular pressure management with eye drops, oral medications, or surgery is necessary. ⁴⁾ Even in late-onset cases more than 15 years after injury, glaucoma can develop, so long-term intraocular pressure monitoring is important.

Precautions in Treatment

• When the b-wave of the electroretinogram disappears, irreversible photoreceptor damage is complete, and visual recovery may not be expected even after IOFB removal. ⁴⁾
• The longer the diagnosis is delayed due to missed foreign body, the more irreversible retinal damage from iron toxicity progresses.
• Even after IOFB removal, continuous management is necessary for residual retinal degeneration and glaucoma.

6. Pathophysiology and Detailed Pathogenesis

Molecular Mechanism of Iron Ion Toxicity

Iron retained in the eye gradually oxidizes and dissolves, diffusing into ocular tissues as iron ions (Fe²⁺/Fe³⁺). The central mechanisms of iron ion-induced cell damage are the following two reaction pathways. ^{4, 3)}

• Haber-Weiss reaction and Fenton reaction: Iron ions catalyze the production of reactive oxygen species (ROS), particularly hydroxyl radicals (·OH). Hydroxyl radicals cause lipid peroxidation of cell membranes, DNA damage, and protein denaturation.
• Mitochondrial damage: ROS-induced mitochondrial dysfunction leads to selective damage to photoreceptors, which have high energy dependence.

Selective Rod Damage

In ocular siderosis, electroretinogram abnormalities are useful for early diagnosis and severity assessment ⁴⁾. Decreased responses under dark adaptation and loss of responses in advanced cases are observed, and it also serves as an indicator for tracking functional recovery after IOFB removal.

Pathogenesis of Glaucoma

Iron deposition in the trabecular meshwork causes mechanical obstruction of the outflow pathway and cytotoxicity ⁴⁾. This increases aqueous humor outflow resistance, leading to secondary open-angle glaucoma. Trabecular damage may persist even after foreign body removal, requiring long-term intraocular pressure management.

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7. Latest Research and Future Perspectives (Research-stage Reports)

For Patients: Please Read Carefully

The following content is currently at the research stage or in clinical trials and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Optimization of Early Diagnosis and Treatment Timing Using Electroretinography

Functional assessment using electroretinography is being studied as an important indicator for determining surgical indications for ocular siderosis. By quantifying the correlation between the degree of b-wave reduction and actual retinal tissue damage, removal of IOFB during the early window when “iron toxicity is present but has not yet led to irreversible damage” may help preserve vision. ⁴⁾

Reversibility of Iron Toxicity

Some reports have observed improvement in electroretinographic findings (approximately 40% partial recovery) when IOFB is removed early. This suggests that when iron ion-induced oxidative stress is mild, tissue function may recover after removal, providing a rationale for early intervention.

Q What happens if IOFB is left in place for a long time?

A

Iron toxicity is persistent and progressive, and if left untreated, visual acuity loss, night blindness, and visual field constriction progress irreversibly. There have been reports of glaucoma developing more than 15 years after injury, ⁴⁾ and long-term follow-up is necessary.

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8. References

1. Parameswarappa DC, Jabeen F, Arunachalam C. Clinical profile, demographic distribution, management and outcomes of ocular siderosis in 58 eyes. Indian J Ophthalmol. 2023;71(2):418-423.
2. Dass AB, Ferrone PJ, Chu YR, Esposito M, Gray L. Sensitivity of spiral computed tomography scanning for detecting intraocular foreign bodies. Ophthalmology. 2001;108(12):2326-2328.
3. Chai X, Li W, Zhao F, et al. Ocular siderosis misdiagnosed as chronic anterior uveitis: a case report. BMC Ophthalmol. 2026;26:102.
4. Hope-Ross M, Mahon GJ, Johnston PB. Ocular siderosis. Eye (Lond). 1993;7(Pt 3):419-425.