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Editor,—A phacoemulsification (phaco) chopper was accidentally damaged by a phaco handpiece during a phaco cataract surgery. A small fragment was suspected to have dropped into the vitreal cavity. The presence of this tiny intraocular foreign body (IOFB) was missed by the orbital x rays and the computed tomography (CT) scan, but was clearly shown on ultrasound B-scan technique. Pars plana vitrectomy was performed and the foreign body (FB) was found and removed. This case demonstrates the potential hazard caused by the powerful phaco energy as well as the usefulness of the B-scan in detecting small size IOFBs, which may be missed by the standard CT scan.
A 72 year old Chinese woman underwent right phaco cataract extraction in December 1996. In the middle of the phaco process, the phaco chopper accidentally came into contact with the tip of the phaco handpiece briefly. No obvious breakage was seen on the chopper and the phaco process was continued. However, when the nucleus removal was completed and the chopper was removed from the eye, it was noted that the chopper had two loose points with two tiny pieces of the instrument easily breaking off from the main body. When these two loose pieces were put back to the breaking points, the instrument appeared to be intact. Missing fragments, however, could not be entirely excluded. A thorough search for any residual fragments in the anterior chamber under the operating microscope did not reveal anything. The residual cortex was then removed with the standard automated irrigation and aspiration technique. Near the end of cortical removal, the vitreal pressure was high and the posterior capsule was accidentally ruptured at a site between the 3 and 6 o’clock positions. In addition to some vitreous loss, the tear extended to beyond the equator resulting in a linear radial tear in the anterior capsule at the 6 o’clock position. Anterior vitrectomy was thus performed. The capsular remnants were thought to be inadequate for a stable placement of a posterior chamber intraocular lens (IOL). The wound was thus closed without IOL implantation but a second stage scleral fixation of IOL was planned.
In order to make sure that no metallic fragments from the chopper were left in the eye, we performed a B-scan study on the eye. A small piece of IOFB was clearly shown (Fig 1). However, there were no vitreous haemorrhage or retinal detachment. An orbital xrays (anteroposterior and lateral views) was done but no radio-opaque FB was found. We went on to evaluate the case further with an orbital CT scan. A spiral CT scan was performed (3 mm collimation, 3 mm/s table speed, 120 kVp, 80 mA) and the images were reconstructed into 1 mm images. No FB could be identified. Subsequently, the patient received a pars plana vitrectomy and removal of residual lens material. The surgeon was also able to visualise and remove the metallic FB (0.1 × 0.3 × 0.6 mm) from the vitreous cavity. The capsular remnants were found to be adequate for sulcus fixation of IOL without suturing. Postoperatively the patient did well with no complications. The CT films were reviewed again retrospectively by the radiologist and no radio-opaque FB was suspected. This eye achieved a visual acuity of 6/9 at the latest follow up, which was 6 months after the incident.
In recent years, phaco surgery has grown to become one of the standard methods of removing cataract in many parts of the world. Many ophthalmologists are using the two handed technique to perform phaco. This technique has been proved to be effective and is well tolerated by the eye. However, there are times when the lens manoeuvre instrument, such as the phaco chopper, comes into contact with the phaco handpiece while the ultrasound is being applied.1 Small metallic fragments may break off from such instruments. The possibility of the presence of metallic fragments from these instruments left in the eye should not be overlooked. Braunstein et al 2reported six cases of intraocular metallic FBs after cataract extraction by the two handed phaco technique. Similar findings have also been produced in vitro by applying ultrasound power from phaco handpiece to a cyclodialysis spatula.2
The above case demonstrates this risk and the way it was managed afterwards. There are several important aspects. Firstly, the phaco surgeon has to be alert and aware of the potential damage to the phaco instruments that may arise when these instruments come into contact with the phaco tip. It would be advisable to take precautions to avoid such contact. Secondly, if such contact occurs during the surgery, the eye as well as the instruments needs to be carefully examined. In our case, although the loose pieces of the phaco chopper seemed to be all present, a tiny piece was in fact still left intraocularly. Thirdly, it is essential to employ appropriate diagnostic tests to evaluate the situation. Sometimes, it is essential to employ multiple imaging modalities to increase the sensitivity of the detection.
CT scan, in most settings, is preferred to B-scan for the demonstration and localisation of FBs in the globe.3 4Lindahl recommended CT scans as the primary diagnostic tool in the detection and localisation of IOFBs.4 In most cases, a 5 mm cut CT scan is already effective enough in diagnosing IOFB when the plain x ray manage to show the radio-opaque FB. A 3 mm cut is recommended if the plain x rays is negative or equivocal.3 5 Reconstruction into 1 mm cut might enhance the chance of detecting small FBs. However, owing to the partial volume effect, tiny FBs smaller than 1 mm might still be missed. B-scan may have a special role in detecting small size IOFBs.6 7 The commercially available B-scanner has an axial resolution of 120 μm, and a lateral resolution of 650 μm. Theoretically, B-scan is capable of detecting objects which are not detectable in the CT scan owing to partial volume effect or if the CT attenuation number of the FB approaches that of its surrounding structure. As demonstrated in our case, the tiny IOFB was clearly shown in the B-scan but missed by the CT scan, despite the fact that the chopper material is metallic and has a CT number of 590. Besides, ultrasound could be extremely useful for localisation of FB when it is anterior to the globe wall, intramural or extrascleral. Additionally, it can also help delineate the extent of associated soft tissue injury.6-8
There are reports describing tiny metallic fragments breaking off from the phaco handpiece in which conservative treatment was recommended.1 2 We opted to remove the FB surgically as the metallic fragment from the chopper in our case is much larger.
Supported in part by the W K Lee Eye Foundation.