Sir,

In pars plana vitrectomy the two active ports are sealed with either gold or silver plated scleral plugs (Figure 1) when performing steps such as scleral depression. Occasionally these plugs cannot be located at the completion of surgery, and are either on the drape, in the suction bottle, on the operating theatre floor or located sub-conjunctively. When vitrectomy is combined with scleral buckling the sub-conjunctival space is opened extensively and plugs can slip posterior to the equator and prove difficult to locate.

Figure 1
figure 1

Gold and silver plated vitrectomy port plugs.

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In conjunction with our Department of Medical Physics and Bioengineering we investigated the magnetic compatibility of these plugs: both gold and silver plated plugs were found to be radio-opaque, and further analysis in a magnetic field revealed that they exhibit considerable ferromagnetism (Figure 2). Consequently their presence in the orbit is an absolute contra-indication to performing MRI scanning in a patient. We therefore recommend that all patients with suspected per-operative loss of scleral plugs be x-rayed postoperatively and if plugs are present, they should be advised against having an MRI scan at a future date.

Figure 2
figure 2

X-ray appearance of the plugs.

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An alternative is to use non-metallic or MRI compatible scleral plugs.