Journal of Neuro-Ophthalmology, March 2015, Volume 35, Issue 1

Bitemporal Hemianopia Secondary to Nasal Staphylomata

The clinical importance of recognizing concurrent RMD and MG is that muscle rippling in this condition improves after immunosuppression (6,7) but worsens af-ter treatment with conventional doses of acetylcholines-terase inhibitors, which likely unmask the muscle hyperexcitability of RMD. As in patients with MG and thymoma, antibodies are directed at the muscle protein titin but at a different site. This case also further high-lights the very low true false-positive rate of acetylcholine receptor antibodies (0.05%) (1), such that even in the absence of clinical symptoms or electrophysiologic find-ings, the presence of these antibodies may anticipate the later development of MG. Dane A. Breker, MD Department of Ophthalmology and Visual Sciences University of Michigan Ann Arbor, MI Ann A. Little, MD Department of Neurology University of Michigan Ann Arbor, MI Jonathan D. Trobe, MD Department of Ophthalmology and Visual Sciences University of Michigan Ann Arbor, MI Department of Neurology University of Michigan Ann Arbor, MI The authors report no conflicts of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the full text and PDF versions of this article on the journal's Web site (www.jneuro-ophthalmology.com). REFERENCES 1. Kosmorsky GS, Mehta N, Mitsumoto H, Prayson R. Intermittent esotropia associated with rippling muscle disease. J Neuroophthalmol. 1995;15:147-151. 2. Ansevin CF, Agamanolis DP. Rippling muscles and myasthenia gravis with rippling muscles. Arch Neurol. 1996;53:197-199. 3. Vernino S, Auger RG, Emslie-Smith AM, Harper CM, Lennon VA. Myasthenia, thymoma, presynaptic antibodies, and a continuum of neuromuscular hyperexcitability. Neurology. 1999;53:1233-1239. 4. Vernino S, Lennon VA. Ion channel and striational antibodies define a continuum of autoimmune neuromuscular hyperexcitability. Muscle Nerve. 2002;26:702-707. 5. Greenberg SA. Acquired rippling muscle disease with myasthenia gravis. Muscle Nerve. 2004;29:143-146. 6. Müller-Felber W, Ansevin CF, Ricker K, Müller-Jenssen A, Töpfer M, Goebel HH, Pongratz DE. Immunosuppressive treatment of rippling muscle disease in patients with myasthenia gravis. Neuromuscul Disord. 1999;9:604-607. 7. Schoser B, Jacob S, Hilton-Jones D, Müller-Felber W, Kubisch C, Claus D, Goebel HH, Vita G, Vincent A, Toscano A, Van den Bergh P. Immune-mediated rippling muscle disease with myasthenia gravis: a report of seven patients with long-term follow-up in two. Neuromuscul Disord. 2009;19:223-238. 8. Torbergsen T. A family with dominant hereditary myotonia, muscular hypertrophy, and increased muscular irritability, distinct from myotonia congenita thomsen. Acta Neurol Scand. 1975;51:225-232. 9. Gazzerro E, Sotgia F, Bruno C, Lisanti MP, Minetti C. Caveolinopathies: from the biology of caveolin-3 to human diseases. Eur J Hum Genet. 2010;18:137-145. 10. Torbergsen T. Rippling muscle disease: a review. Muscle Nerve Suppl. 2002;11:S103-S107. Bitemporal Hemianopia Secondary to Nasal Staphylomata The interesting article by Wang et al (1) seeks to explain the mechanism of bitemporal hemianopia due to chias-mal compression. Our case is a reminder that bitemporal hemianopia may be secondary to refractive optical effects and mechanical effects on the optic chiasm. A 68-year-old woman with an 18-month history of a generalized headache was noted to have a bitemporal visual field defect by her optometrist and was referred FIG. 1. Both optic discs are tilted with less pigmentation of the nasal retina bilaterally. Letters to the Editor: J Neuro-Ophthalmol 2015; 35: 94-105 99 Letters to the Editor Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. urgently to the Ophthalmology Department. Her visual acuities were 20/30 in each eye when corrected for myopia and astigmatism (right eye: 26.2512.00 · 77; left eye: 25.7511.50 · 97). Intraocular pressures were normal in each eye. Ophthalmoscopy showed tilted optic discs with peripapillary atrophy but healthy neuroretinal rims and pale nasal retinas bilaterally (Fig. 1). Automated visual field testing (24-2) with the patient's reading prescription (right eye: 23.0011.75 · 76 left eye: 22.5011.50 · 95) confirmed a bitemporal visual field defect (Fig. 2A). How-ever, confrontation visual fields were full. Brain magnetic FIG. 2. Automated visual fields. A. Bitemporal field loss is present with the patient wearing her reading prescription. B. Visual fields are full with the patient wearing her distance prescription. FIG. 3. T2 axial magnetic resonance imaging reveals ovoid globes nasally. FIG. 4. A. The black line indicates an emmetropic eye, where parallel light is focused onto the retina. The dashed line indicates a myopic eye, where light is focused anterior to the retina. B. In a myopic eye, with use of a concave lens, parallel light is focused onto the retina. In a patient with no staphyloma, the curvature of the eye is spherical. Light falling onto all parts of the retina will be focused through the concave lens. C. In a patient with staphyloma, light is fo-cused on the macula (solid line) but with increased axial length in the staphylomatous segment, light is not focused on the retina (dashed line) causing blurred vision in the corresponding visual field. P, principal plane of the eye. Modified from Elkington AR, Frank HJ, Greaney MJ (6). 100 Letters to the Editor: J Neuro-Ophthalmol 2015; 35: 94-105 Letters to the Editor Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. resonance imaging revealed no abnormalities along the visual pathways but did demonstrate "ovoid" globes (Fig. 3). Optical coherence tomography and B-scan ultra-sonography confirmed nasal staphylomata in both eyes and showed the eyes to be longer from front to back nasally (29.06 mm, right eye, and 31.40 mm, left eye) than tem-porally (27.74 mm, right eye, and 29.04 mm, left eye) The diagnosis of refractive bitemporal visual field defects due to staphylomata was confirmed by repeating the examination with the patient wearing her distance refraction, which abolished the field defects (Fig. 2B). A posterior staphyloma is a protrusion of the posterior wall of the eye (2), commonly associated with high myopia (3), and is known to give rise to visual field defects (4,5). One possible explanation is that nerve fibres are under mechanical tension in the area of the staphyloma which reduces axonal flow impairing optic nerve function (5). An alternate explanation is that the field defects are due to a differing refractive error in the location of the staph-yloma caused by increased axial length (6). Our findings support the latter possibility; we repeated visual field testing with a higher power of the correcting lens, compensating for the staphylomatous refractive error. Light previously defo-cussed over the staphyloma was now in focus and therefore perceived by the patient (Fig. 4). Although a rare cause, bilateral nasal staphylomata should be included in the differential diagnosis of bitem-poral hemianopia. Unnecessary imaging to rule out com-pressive lesions of the optic chiasm could have been avoided by retesting fields with a different refractive correction. Clues to diagnosis were bilateral nasal retinal pallor, visual field defects crossing the vertical midline, and the presence of full fields to confrontation. Anjali Gupta, MBChB Victoria Eye Unit, Wye Valley NHS Trust, County Hospital, Hereford, United Kingdom J. M. Alaric Smith, MBChB, MRCP, FRCOphth Victoria Eye Unit, Wye Valley NHS Trust, County Hospital, Hereford, United Kingdom The authors report no conflicts of interest. ACKNOWLEDGMENTS The authors thank Dr Raveesh Hanasoge, MD, DNB, FRCR, for help with MRI images. REFERENCES 1. Wang X, Neely AJ, McIlwaine GG, Tahtali M, Lillicrap TP, Lueck CJ. Finite element modelling of optic chiasmal compression. J Neuroophthalmol. 2014;34:324-330. 2. Ohno-Matsui K. Proposed classification of posterior staphylomas based on analyses of eye shape by three-dimensional magnetic resonance imaging and wide-field fundus imaging. Ophthalmology. 2014;121:1798-1809. 3. Chang L, Pan C-W, Ohno-Matsui K, et al. Myopia-related fundus changes in Singapore adults with high myopia. Am J Ophthalmol. 2013;155:991-999. 4. Tsatos M, Eke T. Staphyloma causing visual field defect, illustrating the risk of globe perforation with sharp-needle anaesthesia. Eye. 2007;21:857-858. 5. Ohno-Matsui K, Shimada N, Yasumzumi K, et al. Long-term development of significant visual field defects in highly myopic eyes. Am J Ophthalmol. 2011;152:256-265. 6. Elkington AR, Frank HJ, Greaney MJ. Refraction by the eye and optics of ametropia. In: Clinical Optics, 3rd edition. Oxford, MS: Blackwell Science Ltd, 1999:99-121. Reduced Apparent Diffusion Coefficient in Neuromyelitis Optica-Associated Optic Neuropathy In their excellent review of neuromyelitis optica (NMO), Morrow and Wingerchuk (1) discuss the criteria that distinguish this condition from multiple sclerosis. Here, we describe diffusion-weighted magnetic resonance imaging (DWI) of the optic nerve in a patient with NMO-associated optic neuropathy. A 21-year-old man developed vision loss in the right eye that was diagnosed as optic neuritis. After a delay of 5 months, he was referred for neuro-ophthalmology evaluation. Visual acuity was 20/400 in the right eye and 20/20 in the left eye. Visual field testing showed severe depression in the right eye and normal function in the left eye. The right optic disc was pale and the left optic disc appeared normal. Magnetic resonance imaging (MRI) revealed slight atrophy of the right optic nerve, but no demyelinating plaques. A year later, the patient experienced rapidly progressive vision loss in the left eye. The acuity was 20/400 in the right eye and 20/800 in the left eye, with generalized visual field loss in the left eye. The right optic disc was pale and the left optic disc was edematous. The patient was treated intravenously with methylprednisolone, followed by oral prednisone. Serum and cerebrospinal fluid were positive for anti-AQP4 immunoglobulin G, as determined by a cell-based fluorescence assay (2). Three weeks later, acuity in the left eye was 20/80, with improvement in the visual field. MRI of the orbits 4 weeks after the onset of vision loss showed enhancement of the left optic nerve (Fig. 1A), and DWI revealed increased signal along the course of the left optic nerve (Fig. 1B). The apparent diffusion coefficient (ADC) map demonstrated hypointense signal within the left optic nerve (Fig. 1C). The ADC value along a representative 45.6 mm2 segment of the left optic nerve measured 0.875 · 1023 mm2/s and along a 48.4 mm2 segment of the right optic nerve was 1.63 · 1023 mm2/s. DWI obtained a year earlier, Letters to the Editor: J Neuro-Ophthalmol 2015; 35: 94-105 101 Letters to the Editor Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.