Anterior Ischemic Optic Neuropathy After Strabismus Surgery

Abstract

We report a case of nonarteritic anterior ischemic optic neuropathy (NAION) in a healthy young woman after strabismus surgery. A 26-year-old woman with no medical history underwent uneventful left medial rectus recession and lateral rectus resection for a long-standing esotropia under general anesthesia. Preoperatively, visual acuity had been 20/20 in the right eye and 20/200 in the left eye (amblyopia). Thirteen days postoperatively, she noticed loss of vision superiorly in the left eye on awakening without any other symptoms. On our examination the next day, visual acuity was 20/20 in the right eye and 20/400 in the left eye. She had a superior nerve fiber bundle (altitudinal) visual field defect on confrontation, a left relative afferent pupillary defect, and mild left optic disc swelling, mainly inferiorly (Fig. 1). The right optic disc had a normal appearance. Both discs had a cup-to-disc ratio of 0.1. All other aspects of the ophthalmic examination were normal.FIG. 1: Fundus photography performed 1 day after onset of visual field loss shows left optic disc swelling.Results of standard laboratory tests, including a full blood cell count, serum electrolytes, erythrocyte sedimentation rate, C-reactive protein, thyroid function, blood glucose, and anti-nuclear, anti-mitochondrial, anti-smooth muscle, and anti-parietal cell antibodies, were normal. MRI of the brain and orbits was unremarkable. Four weeks later, visual acuity in the left eye had returned to its baseline level of 20/200, but the altitudinal field defect persisted (Fig. 2). A diagnosis of left NAION was made. Six months later, field testing showed a persistent defect with some improvement (Fig. 3).FIG. 2: Late-phase fluorescein angiography demonstrates areas of pinpoint hyperfluorescence without marked optic disc hyperfluorescence.FIG. 3: Visual field examination performed 7 months after the onset of field loss shows minimal improvement.NAION has been reported after anterior segment (mainly cataract) surgery (1), vitrectomy (2), scleral buckling surgery (3), and post-LASIK (4). We have found no reports of NAION occurring either immediately or after an interval following strabismus surgery, although a case of posterior ischemic optic neuropathy has been reported (5). Our patient had no risk factors for NAION apart from a low cup-to-disc ratio, and her youth makes her an unlikely candidate for spontaneous NAION. The ages of patients reported with NAION occurring at an interval after ocular surgery range from 48 to 94 (2,4). A case has been reported after intraocular lens implantation in a 33-year-old woman, but this occurred immediately after surgery rather than after an interval (6). The delayed onset of symptoms in our young patient raises the possibility of an inflammatory etiology. However, the lack of pain and normal MRI scan suggest that optic neuritis was unlikely. Given our patient's left amblyopia, we cannot exclude preexisting structural anomalies that might have increased her susceptibility to NAION. Also, from one case, we cannot conclude that the optic neuropathy and strabismus surgery were necessarily related. O. A. R. Mahroo, MB, BChir, PhD C. J. Hammond, MB, BChir, MD, FRCOphth West Kent Eye Centre Princess Royal University Hospital Farnborough Common Orpington, UK [email protected]