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Editor,—The precise imaging of anteriorly located intraocular foreign bodies (IOFBs) is difficult with present techniques—namely, computed tomography (CT) scanning, and A and B scan ultrasonography. In this case, ultrasound biomicroscopy (UBM) proves itself to be an excellent imaging technique for these IOFBs and therefore useful in clinical practice.
A 79 year old man presented to the eye casualty department complaining of a painful, red left eye with reduced vision. Two weeks previously he had been hit in that eye by the end of a nail which he had been pulling out of a table. He believed he had removed the piece of metal from his eye at the time. On examination, visual acuity (VA) was 6/9 in the right eye and 6/60 in the left eye. There was a nasal subconjunctival haemorrhage, though the entry wound was found at 5 o’clock, extending radially from the cornea to the scleral border of the limbus and was siedle negative. There was an anterior uveitis with cells ++ and flare ++, and 360 degree posterior synechiae. There was brisk vitreous activity, cells ++, and poor fundal view. Intraocular pressure was 12 bilaterally. Gonioscopy revealed iris tissue up to the wound but no foreign body in the anterior chamber. Plain skull x ray (Fig 1A) showed an intraocular radio-opaque foreign body. The patient was admitted for intense dilatation and steroid treatment before surgery. Superotemporal posterior synechiae were broken and some fundal view was obtained—BIO 3, though the IOFB was not seen. Conventional A and B scan ultrasound failed to localise accurately the foreign body, although it was identified on extreme peripheral sections (Fig 1B). CT scan showed a densely radio-opaque IOFB but accurate localisation was not possible.
The wound had been present for 2 weeks, was self sealing, and it was considered safe to perform UBM using a standard eyecup, which had been disinfected using Milton. This identified a foreign body (Fig 1C,D) adjacent to pars plana, 4 mm posterior to the angle recess (that is, 5 mm posterior to limbus) at the 5 o’clock meridian. When surgery was performed, a scleral trap door was constructed and a giant magnet was then placed with its point 5 mm from the limbus at the 5 o’clock meridian. The metallic foreign body was removed with ease. The scleral flap was then sutured. Cryotherapy was then applied to the entry site and the peripheral retina was inspected for any evidence of tears. In addition, perioperative systemic and topical steroids were administered to control intraocular inflammation and prevent proliferative vitreoretinopathy (PVR). Unfortunately, 6 weeks later he developed a total retinal detachment with inferior PVR, despite perioperative control of intraocular inflammation with systemic steroids, and further surgery was required.
The accurate localisation of IOFBs is essential for the optimum management of patients. This enables the surgeon to plan the most atraumatic method of removing the IOFB during surgery. Anteriorly located foreign bodies are particularly problematic as it may be impossible to visualise them directly although indentation can aid direct visualisation of those located at the retinal periphery. At present, imaging of these IOFBs is possible with conventional A and B scan ultrasonography, plain x ray and CT scanning. CT scanning has its limitations owing to image obscuration from eye movement and the quality of images reconstructed by computers,1 2 although newer methods have been developed in an attempt to overcome these factors.3 A and B scan ultrasonography, although sensitive in detection and localisation of posterior segment IOFBs, does not provide good resolution of the extreme retinal periphery, ciliary body, posterior chamber, and drainage angle whereas UBM has good resolution of these areas.4 UBM can prove a useful tool to pinpoint the location of anteriorly located IOFBs as has been shown in experimental models.5 6 This case highlights the use of UBM in clinical practice.