Visual outcome and prognostic factors after magnetic extraction of posterior segment foreign bodies in 40 cases

To evaluate the clinical features as well as the visual and anatomical outcome in eyes with magnetic posterior segment foreign bodies, to identify prognostic factors after removal using an electromagnet.

The records of 40 patients with posterior segment foreign bodies were retrospectively reviewed for 6 years (1989-94). Post-traumatic cataracts and secondary retinal detachments were treated using conventional surgical techniques. Pars plana vitrectomy was used only for late complications. The mean follow up was 30 months (6-71). Clinical factors were studied using univariate analysis.

The most common findings before treatment of these 40 eyes were lens wound, hyphaema, vitreous haemorrhage, and retinal impairment. The foreign body was in the vitreous (85%) or minimally embedded in the retina (15%). Initial visual acuity was worse or equal to 20/40 in 70% of the cases. Subsequent to surgical treatment, a cataract was reported in 60% of the patients. Postoperative complications included retinal detachment (15%) and phthysis (5%). The prognosis was worse in cases with intraocular foreign body of largest diameter > or = 3 mm, an initial visual acuity less than 20/200, or the presence of post-traumatic retinal detachment. Presence of initial intravitreous haemorrhage, hyphaema, or intraocular tissue prolapse did not appear to affect the prognosis.

The long term visual acuity results indicated that wound repair associated with conventional magnet extraction in an emergency is a viable treatment for posterior segment magnetic foreign bodies in this selected group. At the time of diagnosis, size of foreign body (< 3 mm) and initial visual acuity > or = 20/200 were predictors of good visual outcome after primary magnetic extraction.