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

Abstract

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.

Highlights

• •We observed a case of a subretinal iron foreign body mistaken for a blood clot and which was not diagnosed during the initial vitreous surgery.
• •Ocular siderosis subsequently developed more than a year after injury.
• •Siderosis may develop over the long term. Surgical removal should be actively considered if a subretinal iron foreign body is suspected.
• •X-rays and/or CT scans should be obtained in the early stages of treatment even if there is no obvious evidence of a foreign body.

1. Introduction

Ocular siderosis occurs when an intraocular foreign body containing iron remains in the eye for a long period of time, which can lead to blindness due to widespread toxicity.¹ The onset of siderosis varies greatly from case to case, with previously cases reporting onset as early as two months after injury and to as late as 15 years after injury.^2,3 In many cases, a foreign body can be detected by taking a detailed medical history and performing a comprehensive ophthalmologic examination, but there are also cases in which the foreign body is overlooked.⁴

Here, we report a case of a subretinal iron foreign body not diagnosed during the initial vitreous surgery, which later led to ocular siderosis more than a year after the initial injury.

2. Case

A 30-year-old Asian male, a construction worker, was injured by a small piece of shrapnel during work and visited an eye clinic due to decreased left vision on day X. He was referred to our hospital with a diagnosis of left vitreous hemorrhage on day X+1. At the initial visit, the best-corrected visual acuity (BCVA) was 20/16 in the right eye and 20/600 in the left eye, the intraocular pressure was 14 mmHg in the right and 9 mmHg in the left eye, and fluorescein dye staining for the left eye revealed a conjunctival laceration, but the Seidel test was negative with no obvious scleral wounds. The fundus was difficult to observe due to the vitreous hemorrhage (Fig. 1A), and ocular ultrasound examination detected no obvious foreign bodies. On X+1 month, the vitreous hemorrhage subsided naturally and the BCVA improved to 20/16 in the left eye (Fig. 1B). At this point, there was no obvious foreign body in the eye. We found a retinal tear at 2 o'clock, but did not perform retinal photocoagulation due to scarring around it. The patient was then lost to follow-up.

Fig. 1.

Fundus images before retinal detachment surgery. On day X+1, the fundus was difficult to observe due to vitreous hemorrhage (A). After X+1 month, the vitreous hemorrhage spontaneously subsided (B). After X+3 months, a rhegmatogenous retinal detachment from 2 o'clock to 9 o'clock was observed (C).

After X+3 months, the patient returned to our hospital due to a decrease in vision to 20/25 in the left eye. We observed a rhegmatogenous retinal detachment (without macular detachment) from 2 o'clock to 9 o'clock in the left eye, with a scarred retinal tear at the 2 o'clock position and an atrophic retinal hole at the 6 o'clock position (Fig. 1C). On the same day, we performed lens-sparing vitrectomy on the left eye. We noticed a black elevated lesion under the retina near the inferior arcade vessels intraoperatively, which we considered to be a blood clot because there was no obvious foreign body in the previous fundus examination (Fig. 2). The surgery was completed with total replacement with 20 % SF₆. At X+5 months (2 months after retinal detachment surgery), the vision recovered to 20/16 in the left eye. Although we observed no morphological changes or other changes such as hemolysis in the subretinal black lesion, the color and OCT findings were considered to be different from a hemorrhage and an intraocular foreign body was suspected (Fig. 3A).

Fig. 2.

Fundus image during retinal detachment surgery. A black elevated lesion under the retina below the macula was observed. Retrospectively, an iron foreign body lurking under the peripheral retina is thought to have migrated to the posterior pole due to gravity when the retinal detachment occurred.

Fig. 3.

Fundus images and optical coherence tomography (OCT) after retinal detachment surgery. Two months after retinal detachment surgery, no change was observed in the subretinal black lesion, and there appeared to be blurring of the retinal layer structure (A). Eight months after retinal detachment surgery, the subretinal lesion changed from black to reddish brown (B). Ten months after retinal detachment surgery, the subretinal lesion changed from reddish brown to brown, and OCT showed no remarkable changes (C). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

At X+11 months (8 months after retinal detachment surgery), the color of the subretinal lesion changed from black to reddish brown (Fig. 3B). At X+13 months (10 months after retinal detachment surgery), the BCVA decreased from 20/20 to 20/30 in the left eye. Slit-lamp examination revealed yellowish brown rusty materials on the surface of the crystalline lens (Fig. 4), while fundus examination showed that the subretinal lesion had changed from reddish brown to brown. Faint vitreous opacity also appeared (Fig. 3C).

Fig. 4.

Anterior segment image at the start of phaco-vitrectomy surgery. Multiple yellowish brown, irregular, minute dots were observed on the lens, which were thought to be rust materials. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Goldmann perimeter revealed an absolute scotoma superiorly corresponding to the macular foreign body (Fig. 5A). Electroretinogram showed significant attenuation with all stimuli (Fig. 6A). Head CT revealed a small area of high absorption at the posterior part of the eyeball, consistent with findings of a subretinal iron foreign body. Based on the above, we thought that ocular siderosis due to a subretinal iron foreign body had developed. At X+14 months, we performed phaco-vitrectomy to remove the subretinal foreign body. We made an intentional break with diathermy directly above the dark elevated lesion, and the foreign body was successfully removed using an intraocular magnet and surgical forceps. Laser photocoagulation was performed on the surrounding retina. Postoperative quantitative analysis of the foreign body using electron microscope X-ray microanalysis revealed that it contained a large amount of iron (Fe) (Fig. 7).

Fig. 5.

Goldmann perimeter results. An absolute scotoma above the retina was observed, corresponding to the presence of a foreign body in the macula. Loss of sensitivity on the nasal side due to superior NFLD was also observed after peripheral retinal detachment (A). The upper visual field defect in the macula, corresponding to the location of the foreign body, expanded (B).

Fig. 6.

Electroretinogram results. Preoperative electroretinogram showed loss of rod response, attenuation of a-wave and b-wave to flash stimulation, loss of OP wave, and marked attenuation of cone response, suggesting widespread retinal damage (A). Postoperative electroretinogram showed no significant changes compared to preoperative results in any of the responses (B).

Fig. 7.

Simple quantitative analysis results (Weight %) and chart using electron microscope X-ray microanalysis. A large amount of iron (Fe) was detected in the sample (Table). The spectrum showed characteristic X-rays representative of Fe (Figure, horizontal axis as energy (kiloelectronvolts), vertical axis as number of detected photons (count number)).

At X+17 months (3 months after the subretinal foreign body removal surgery), Goldmann perimeter showed that the upper visual field defect in the macula corresponding to the location of the foreign body had expanded (Fig. 5B). At X+21 months (7 months after the subretinal foreign body removal surgery), the electroretinogram had no changes (Fig. 6B), and the BCVA showed no improvement at 20/63 in the left eye at X+24 months (10 months after the subretinal foreign body removal surgery).

3. Discussion

In this case, the patient underwent vitreous surgery for retinal detachment 3 months after ocular trauma caused by a foreign body. A subretinal foreign body was first identified during the retinal detachment surgery but was not removed since it was considered to be a blood clot, as there was no obvious foreign body in the previous fundus examination. Retrospectively, it is possible the intraocular foreign body that was present somewhere in the retina may have migrated under the detached retina. The scarred retinal tear at the 2 o'clock position appeared discolored, which may have masked retinal pigment epithelial changes at the possible entry site. The vision remained stable for a long time even after the initial surgery, but ocular siderosis due to the subretinal iron foreign body developed and was then diagnosed a year after the injury. Although we successfully performed surgery to remove the foreign body, the vision did not improve even after the removal.

The onset of ocular siderosis is related to the severity of the intraocular toxic reaction, and it varies with the shape and size of the foreign body, its iron content, and the amount of time it remains in the eye.² Hope-Ross et al.² and Sneed and Weingeist⁵ reported cases that were detected after longer periods of time, at 24 and 40 months, while a case diagnosed 12 years after the initial injury was also reported.⁶ Previous reports have shown that foreign bodies are often removed within 24 hours after injury.⁷ In our case, the foreign body developed ocular siderosis 10 months after being identified, and was removed 14 months after the injury, which is a notably delayed removal compared to the typical time frame.

It has been reported that after removal of an iron foreign body, visual acuity and electroretinograms improve in 78 % of cases.⁶ Our patient underwent surgery in expectation of visual acuity improvement, but postoperative visual acuity was poor and the electroretinogram did not improve. Factors associated with poor visual prognosis include decreased visual acuity at first visit, presence of retinal detachment at first visit, subretinal location, damage to optic nerve and macula before surgery, and a long interval between injury and foreign body removal.^8,9 In our case, the poor visual acuity may be explained by the subretinal location and the long interval between injury and foreign body removal (14 months).

This case serves as a cautionary tale. Since no obvious entry wound was observed immediately after the injury, the subretinal foreign body was judged to be a blood clot and was not removed. Although a few cases of ocular siderosis developing after a long period of time have been reported,^2,3,6 constant caution is necessary even in cases in which vision has remained good for a long time, as in our case. As residual intraocular foreign bodies have a wide range of toxic effects on the eye that have been proven electrophysiologically and histopathologically, removal rather than conservative observation is recommended once diagnosed.²

It is also important to keep in mind when interpreting this case that the patient was a foreign worker without an interpreter. Moyce and Schenker point out the higher risk of work-related injuries when immigrants do not speak the primary language.¹⁰ In addition, the medical history may have been insufficient due to discontinuation of visits. Even if no wound was found, it would be favorable to perform detailed imaging such as head CT scan if the medical history suggests even the slightest possibility of an intraocular foreign body.¹¹ If radiation exposure from CT scans is a concern, routine ultrasound examinations¹² or even plain X-ray examinations,¹³ which involve less radiation exposure, are also suitable alternatives. However, in this case, the small iron foreign body was missed on ultrasound at the initial consultation and was subsequently detected on a CT scan. This suggests that, ultimately, an initial CT scan should be considered whenever circumstances permit.¹¹

4. Conclusion

Subretinal iron foreign bodies may be mistaken for blood clots. As siderosis may occur over the long term even if vision is stable, immediate surgical removal is necessary if a subretinal iron foreign body is suspected.

CRediT authorship contribution statement

Juo-shiuan Lin: Writing – original draft, Visualization, Investigation, Data curation. Takashi Nagamoto: Writing – original draft, Project administration, Conceptualization. Norimitsu Ban: Writing – original draft, Supervision, Project administration, Conceptualization. Motohiro Moriya: Writing – review & editing. Xiaoyan Jiang: Writing – review & editing. Hiromitsu Kunimi: Writing – review & editing. Yohei Tomita: Writing – review & editing. Toshihide Kurihara: Writing – review & editing. Hajime Shinoda: Writing – review & editing. Kazuno Negishi: Writing – review & editing, Supervision.

Patient consent

Consent to publish this case report has been obtained from the patients in writing.

Authorship

All authors attest that they meet the current ICMJE criteria for Authorship.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.