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Gamma knife radiosurgery has been found useful for treatment of trigeminal neuralgia (TN).1–4 Although it is generally safe and well tolerated by most patients, adverse effects have been reported.1–6 Potential ocular complications include “dry eye” and “corneal numbness.”5,6 We describe a case of vision loss that occurred 9 months after gamma knife radiosurgery for TN.
A 68 year old man presented in September 2003 with 3 weeks of fluctuating blurred vision in the right eye. The blurring began 3 weeks earlier and had been preceded by complete numbness of the right side of his face for 1 week.
The patient’s medical history was remarkable for right sided TN that began in 1998, predominantly involving the V2 dermatome. It had been managed medically at first but eventually became incapacitating and led to hospital admission.
In December 2002, he had undergone gamma knife radiosurgery (Leksell Gamma Knife; Elekta Inc, Norcross, GA, USA). The dose matrix grid was 0.6 mm and the right trigeminal root entry zone was targeted tangential to the brainstem. The prescription dose was 40 Gy to the 50% isodose line. A single run with a single shot (treatment time, 29.25 minutes) used a 4 mm collimator. Within days, the patient had clinically significant improvement in symptoms, was pain free, and required no pain medication.
The patient also had a history of chronic renal failure requiring dialysis three times weekly, hypertension, a myeloproliferative disorder, prostate cancer, and hyperlipidaemia. In 1998, he had resection of a left frontal lobe meningioma. His ocular history included bilateral cataract surgery but no history of herpes zoster or herpes simplex.
On initial examination, his vision measured 20/25 right eye and 20/25 left eye. Slit lamp examination of the right cornea revealed a fine punctate epitheliopathy (fig 1A). Corneal sensation, tested with a Cochet-Bonnet aesthesiometer (Luneau Ophtalmologie, Chartres Cedex, France), was absent even at a 5 mm filament length, both subjectively and by blink reflex. Sensation in the left cornea was present at a 60 mm filament length.
The patient’s vision gradually declined despite treatment with preservative free artificial tears and placement of a punctal plug in the right lower lid. Ten weeks after presentation, his vision measured 20/200 right eye and 20/25 left eye. Slit lamp examination revealed severe epithelial keratopathy in the right eye (fig 1B). Fourteen months after radiosurgery, T2 weighted magnetic resonance imaging showed increased signal intensity in the anterior aspect of the right fifth nerve (fig 2).
A punctal plug was placed in the right upper lid. The patient began using topical serum tears four times daily. Partial tarsorrhaphy was discussed with the patient but declined. During the next 6 weeks, the corneal surface improved, and at last follow up the patient’s vision was 20/60.
Gamma knife radiosurgery is an effective treatment for TN with few complications.1–4 Pollock et al6 noted an increased incidence of “trigeminal dysesthesia” and “corneal numbness” after high doses (90 Gy) of gamma knife radiation. In an animal model, a 100 Gy dose caused nerve necrosis.7 Matsuda et al5 identified a “dry eye complication” of epithelial keratopathy after gamma knife radiosurgery for TN. Despite these documented ocular side effects, no cases of vision loss have been reported.5,6
Neurotrophic keratopathy has been recognised in patients with herpes simplex, herpes zoster, and after laser in situ keratomileusis (LASIK) surgery.8–10 Mild neurotrophic keratopathy may be manifested as a punctate epithelial keratopathy. In severe cases, corneal decompensation can lead to severe vision loss.
Our patient had a vision loss to 20/200 associated with the onset of right sided facial numbness 10 months after low dose (40 Gy) gamma knife radiosurgery for TN. Although high dose radiosurgery (90 Gy) is a known risk factor for complications with gamma knife radiosurgery, the low dose our patient received has not been associated with such complications. Patients undergoing gamma knife radiosurgery for TN should be warned of this potential complication and should be evaluated preoperatively and postoperatively by an ophthalmologist.