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Magnet-assisted pars plana vitrectomy for giant metallic intraocular foreign body

¹Retina and Vitreous Section, Department of Ophthalmology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto-SP, Brazil; ²Instituto de Física de São Carlos – USP, São Carlos- SP, Brazil.

Correspondence: Professor Dr Rodrigo Jorge
Email: rjorge{at}fmrp.usp.br
Fax: +55-16-6022860

Date of acceptance: September 1, 2005

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Introduction

Open globe injuries accompanied by an intraocular foreign body (IOFB) are one of the major cause of visual loss in children and young adults.[1,2] Seventy-five percent to 90% of all IOFBs are metallic, and 55% to 80% of these are magnetic. Metallic IOFBs, such as iron and copper, are well-known bioactive substances that are toxic to the retina and must be removed. For these reasons and the frequent association of severe endophthalmitis, it is the standard of care to remove IOFBs as soon as possible.

Magnets have played an important role in the extraction of posterior segment intraocular foreign bodies. Advances in vitreoretinal techniques have led to a change in the management of magnetic metallic IOFB from being an external approach (external electromagnet) to that of an internal one, using pars plana vitrectomy and an intraocular forceps.[3,4] In the case presented here, vitrectomy with external electromagnet (EEM) provided better control for IOFB removal.

Technique

After peribulbar anesthesia, an encircling 42-band was initially placed anterior to the equator. A standard infusion line was placed in the inferotemporal quadrant, with another standard sclerotomy in the superotemporal quadrant. The superonasal sclerotomy was enlarged to 3 mm at the level of the IOFB entry site. The intra-ocular foreign body, a 14-mm sewing needle, was visualized using a wide-angle visualization system (Volk, Mentor, OH) and an OPTO’s reinversor system (OPTO, São Carlos, Brazil). The EEM tip was placed at the site of the nasal sclerotomy and, after a single foot pedal press, the foreign body was directly attracted to the EEM tip and pulled out of the eye in a few seconds. Standard pars plana vitrectomy was then performed to remove vitreous hemorrhage. Additional laser was applied at the foreign body retinal impact site, inferonasal to the optic nerve. Retinal periphery was then inspected and balanced salt solution used as vitreous substitute, without gas tamponade.

Discussion

A traditional magnet intra-ocular forceps could have been used in this case. However, the forceps might have been insufficient to firmly hold the foreign body. As a consequence, the large foreign body (14 mm) would drop and damage healthy retina. A nonmagnetic grasping intra-ocular forceps would also be an interesting alternative. However, the great extension of this sewing needle would make the maneuvers for its removal very dangerous for retina and lens integrity. For this reason, we opted for the removal of this magnetic foreign body by external magnet-assisted pars plana vitrectomy. This method avoids forceps maneuvers inside the vitreous cavity and uses a powerful magnet that would definitely attract and firmly hold the foreign body, minimizing the risks of foreign body drop back. The nasal sclerotomy was made 3.5 mm from the nasal limbus, very close to the entry site, so that the foreign body could be removed along a similar path as the path of entry. This sclerotomy was also enlarged (3 mm) so that we could insert the EEM tip inside the vitreous cavity and the foreign body would not be entrapped during the removal maneuver.

A cylindrical foreign body tends to align its axis with the magnetic field lines similar to a magnetic needle that align to the earth magnetic field line that connect the north to the south poles of our planet. The magnetic field lines of the EEM tip stick out coaxially from its tip end and for that reason, after insertion of the EEM tip and its activation, the foreign body came with its axis parallel to the tip, avoiding rotations inside the vitreous cavity that could damage the lens and the retina.

The pars plana vitrectomy allowed complete control of the removal procedure. In addition, any retinal break would be promptly treated, vitreous hemorrhage was completed removed and additional laser burns could be performed around the initial retinal lesions in the inferior retina.

Finally, the procedure allowed the removal of a large magnetic foreign body in a few seconds with minimal trauma. The use of an intra-ocular forceps may require a bimanual technique, additional sclerotomies, and intravitreal maneuvers, increasing the operative time and the risk of retinal breaks and giant retinal tears.5
For the reasons presented above, external magnet-assisted pars plana vitrectomy provides a controlled and safe removal of large magnetic IOFB(s) in a fast and practical fashion, being a reasonable alternative for the removal of these foreign bodies.

Conflict of Interest Statement

The authors have no proprietary interests in any of the products cited in this paper.

References

• Shock JP, Adams D. Long-term visual acuity results after penetrating and perforating ocular injuries. Am J Ophthalmol. 1985;100:714-718.
• Soheilian M, Ahmadieh H, Sajjadi H, Azarmina M,Miratashi AM, Peyman GA. Temporary keratoprosthesis for surgical management of complicated combined anterior and posterior segment injuries to the eye: combat-versus noncombat-injury cases. Ophthalmic Surg. 1994;25:452-457.
• Bustros SD. Posterior segment intraocular foreign bodies. In: Shingleton BT, Hersh SP, kenyon KR, eds. Eye Trauma, 1st edn. St Louis: Mosby, 1991;226-235.
• Chow Dr, Gasseston BR, Kuczynski B et al. External versus internal approach to the removal of metallic foreign bodies. Retina 2000;20;364-369.
• Soheilian M, Abolhasani A, Ahmadieh H, Azarmina M, Dehgan MH, Mashavekhi A, Siadat F, Moshfegui AA, Peyman GA. Management of magnetic intravitreal foreign bodies in 71 eyes. Ophthalmic Surg Lasers Imaging 2004;35:372-378.