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Sir,

Intraocular foreign bodies are not uncommon. We frequently see the patient with a red eye who has been hammering without eye protection. However, not all patients give such a clear history and it is of major importance that a foreign body is not missed especially by casualty departments. We present two case reports which highlight the need for vigilance and a high index of suspicion even if the plain X-ray is clear.

Case report 1

A 30-year-old white man had been working with a valve on a high-pressure gas cylinder when a blast of high-velocity gas hit his right eye. He had attended the local casualty department on two occasions since with a gritty red right eye. His orbital X-rays did not show any foreign body (Figure 1a). His symptoms persisted and after two weeks he was referred to the ophthalmic department. Snellen vision was 6/5 and the eye was mildly injected. There was a small faint corneal scar with an upward track at the 4 o' clock position near the limbus which was felt to be an entry site. Gonioscopy revealed a foreign body in the inferior angle. He underwent removal of a metallic foreign body with uncomplicated recovery. Snellen vision remains 6/6.

Figure 1
figure 1

(a) Plain orbital X-ray of patient 1. No foreign body is detected. (b) Plain orbital X-ray of patient 2. Again no foreign body is demonstrated.

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Case report 2

A 40-year-old white man was referred to the ophthalmology department 1 month after a foreign body struck his right eye while hammering a steel nail. Plain X-rays failed to show an intraocular foreign body (Figure 1b), but he suffered persistent blurring of vision in the right eye. He was noted to have a small, axial, full thickness central corneal scar, with some pigment on the anterior lens surface. Snellen vision was 6/6. Gonioscopy revealed a foreign body in the inferior angle. He underwent surgical removal of this foreign body. Recovery was uneventful and vision remains 6/6.

In both cases, the surgical technique involved dissection of a small scleral flap at the 6 o' clock position with dissection into the anterior chamber and direct removal of the foreign body with forceps (Figure 2a and b).

Figure 2
figure 2

(a) Surgical technique demonstrating removal of foreign body (patient 2). (b) Photograph of the foreign bodies removed during surgery. Left = case 1 and right = case 2.

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Comment

These two cases highlight the fact that a plain X-ray will not exclude with certainty an intraocular foreign body. Any patient with a significant history should be viewed with a high index of suspicion and a plain X-ray does not replace thorough clinical examination including gonioscopy. Davidson and Sivalingam1 reported a similar case of a foreign body in the anterior chamber angle which was eventually discovered after gonioscopy was performed because of the high clinical suspicion.1

Our two cases reinforce the fact that plain X-rays are of limited value when dealing with suspected intraocular foreign bodies (IOFB). The overall detection rate of foreign bodies for plain X-rays has been reported as low as 40% with particularly poor pick-up rates for graphite, wood, and perspex.2 Metallic foreign bodies can also be missed.2, 3 This is an important issue when considering screening before MRI scanning, as ocular damage has been reported if a metallic IOFB is undetected. The movement of the metallic fragment within the magnetic field has been found to cause problems such as cataract and hyphaema.3, 4 Lagalla et al5 compared plain X-ray, CT, and MRI capabilities in IOFB detection in vitro and in pig eyes. They recommend that CT scanning is the preferred investigation when it is necessary to exclude an IOFB.5 However, even then there have been isolated reports of the failure of computed tomography to find metallic foreign bodies.6, 7Modern spiral CT scanning techniques offer a shorter examination time (than previous conventional CT scanning). Good sensitivities with 3 mm cuts have been reported to match 1 mm cuts in sensitivity of detection of small glass, stone and metallic IOFBs.8, 9

In these two cases, the foreign body was located in the anterior chamber. Ultrasound biomicroscopy has been described as a useful tool in this situation. 50 MHz ultrasound method when available enables imaging of anterior segment details at high resolution up to about 5 mm depth. It has been reported to detect IOFBs even when CT scanning failed.10, 11 However, it is recommended only as a second-line investigation once computed tomography has failed to give the desired answers or as an initial investigation in small, nonmetallic anteriorly located intraocular foreign bodies.11

In conclusion, these two patients highlight the importance of good clinical examination including gonioscopy when there is suspicion of an intraocular foreign body. Plain X-ray cannot be relied upon and CT with or without ultrasound biomicroscopy should be performed to help detect anterior segment foreign bodies if they cannot be found clinically. We need to emphasise this fact to accident and emergency department clinicians to avoid missed diagnoses.