Anterior segment optical coherence tomography in intracorneal foreign body.

Introduction

Corneal foreign bodies have been reported to be the second most common type of eye injury, comprising approximately 30.8% of ocular injuries.[1] Most injuries are mild and do not cause significant ocular morbidity or loss of work. The majority of corneal foreign bodies can be prevented by appropriate eyewear. Anterior segment optical coherence tomography (AS-OCT) is a valuable tool in the early diagnosis and monitoring of treatment progress in cases of ocular trauma.[2] However, its value in corneal foreign bodies has not been investigated. We describe the case of a young male with an intracorneal foreign body and highlight the role of AS-OCT in the management.

Case Report

A 24-year-old male presented to the emergency complaining of a foreign body sensation in his right eye. Four hours earlier he was working in his garage and felt “something” fly into his eye. He was not wearing any protective eyewear. On examination, the patient's visual acuity was 20/20 unaided in both eyes. Slit lamp examination revealed a thin, curved metallic foreign body (FB) embedded in the cornea about 1 mm superior to the center of the cornea [Figure 1a]. It appeared to be a wire with the longer anterior part lying outside the surface of the cornea. The posterior part was either in the corneal stroma or was protruding into the anterior chamber (AC) [Figure 1b]. There was no apparent iris or lens damage and no cells or flare were detected in the AC. Dilated examination of the fundus revealed no abnormality. Examination of the right eye was unremarkable with a visual acuity of 20/20.

Figure 1

(a) Clinical photograph of the patient at presentation showing a thin, curved metallic foreign body (FB) embedded in the cornea of the right eye about 1 mm superior to the center (b) At higher magnification, it appeared to be a wire with the longer anterior part lying outside the surface of the cornea and the posterior part either in the corneal stroma or protruding into the anterior chamber (AC) (c) Anterior segment optical coherence tomography (AS-OCT) showing shadowing of the corneal layers corresponding to the location of the FB (d) A hyper-reflective lesion was picked up in the AC posterior to the cornea, suggesting that the FB had penetrated the full thickness of the cornea and that a part of it extended into the AC

Anterior segment optical coherence tomography (AS-OCT) was performed in the right eye using RTVue-100 OCT (Optovue, Inc., Fremont, California, USA) with a corneal adaptor module (CAM). It showed shadowing of the corneal layers corresponding to the location of the FB [Figure 1c]. In addition, a hyper-reflective lesion was observed in the AC posterior to the cornea [Figure 1d], suggesting that the FB had penetrated the full thickness of the cornea and that a part of it extended into the AC. Observation of the anterior chamber angle showed no abnormality.

After obtaining informed consent, the patient was taken up for removal of the FB in the operating room under topical anesthesia. Based on the AS-OCT findings, it was planned to remove the FB through the internal route. The pupil was constricted preoperatively with topical Pilocarpine (2%) to prevent lens damage during the procedure. A paracentesis was made to fill the AC with Healon GV. End grasping intraocular forceps were then used to remove the FB taking care that it was removed in the same direction in which it had entered. The AC was washed to remove any viscoelastic and the port hydrated. Because the penetration line was small and oblique and seemed to close without any suture, the eye was closed with a tight bandage. Postoperatively, treatment began with topical antibiotics, artificial tears, and ointment. At one week postoperatively, the patient was asymptomatic with visual acuity of 20/20 and the cornea healed without scarring [Figures 2a and b].

Figure 2

(a) Post operative photograph at one week showing clear cornea with no scarring (b) AS-OCT showing mild corneal thickening at the site of the FB

Comment

ASOCT is a non-contact method of anterior segment imaging. Higher resolution (5 μm) and faster speed of A-scan (26,000 scan/ sec) can be obtained with the 840-nm spectral domain OCT (RTVue-100; Optovue, Inc., Fremont, CA) as compared to the 1,310-nm time domain OCT.[3]

In ocular trauma, AS-OCT results can be used to support diagnosis of ocular surface injuries and monitor the healing process after surgical repair. In addition, it may reveal unexpected lesions that are invisible or difficult to recognize in routine slit-lamp examination.[2]

In this case, preoperative AS-OCT confirmed that the wire had penetrated the full thickness of the cornea and that a part of it protruded in the AC. This was not clear on slit lamp examination because of image overlap. This finding enabled the surgical decision of attempting the FB removal through the internal route, which was successful in atraumatically removing the wire from the cornea. Although high-frequency ultrasound biomicroscopy could have revealed such clinical information, it would be unsuitable in a case with perforating eye injury, because of the pressure induced by the water bath and the risk of contamination.[4]

To conclude, AS-OCT is a novel imaging modality, which is useful in the management of ocular injuries especially where a noninvasive method of anterior segment assessment is required. Our case highlights its utility in the management of intracorneal foreign bodies and in planning the method of FB removal.