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Show Journal of Neiim- Ophthalmology 18( 4): 242- 245, 1998. © 1998 Lippincoll Williams & Wilkins, Philadelphia Monocular Band Optic Atrophy Roger E. Turbin, M. D., Leslie St. Louis, M. D., Dai Barr, F. R. C. O., and Mark J. Kupersmith, M. D. Band or " bow tie" optic atrophy is characterized by well-described ophthalmoscopic findings in the optic nerve and nerve fiber layer and homonymous hemianopia. It is typically associated with compressive lesions of the pregeniculate post-chiasmal visual pathway or, less commonly, congenital malformations affecting the postgeniculate radiations or cortex. A unique case with band optic atrophy is described because of the unilateral visual defect. The optic atrophy is strictly unilateral and without an obvious structural lesion that could explain the optic disc damage. However, incidental cerebral gray matter cortical heterotopia may mark a congenital insult that contributed to both of these abnormal findings. Key Words: Band optic atrophy- Cerebral heterotopia- Optic tract compression. CASE REPORT An 1 1 - year- old boy was evaluated for poor vision and a chronic inward- turned left eye. Three years earlier, he had been treated with a patching regimen for strabismic amblyopia. Review of records showed visual acuity of 20/ 40 OD, 20/ 160 OS, left esotropia of 8 prism diopters and " cupping," with no further details recorded about his left optic disc. On current examination, best corrected distance visual acuity was 20/ 20 OD (- 1.25- 1.50 x 65°) and 20/ 200 OS ( plano- 1.50 x 100°). Color vision evaluated by Ishihara isochromatic plates was normal in the right eye and variable in the left, with 5/ 10 to 8/ 8 plates identified in different sets of plates. Findings in an anterior segment examination were normal. Applanation tonometry was symmetric at 16 mm Hg. The pupils were 4 mm, symmetric, round, and reactive to light. The left pupil had a sluggish consensual response to light and a moderate relative afferent defect. A motility examination revealed full versions without nystagmus, normal saccades, and concomitant left esotropia of 30 prism diopters. Ophthalmoscopy showed a tear drop- shaped right optic nerve Manuscript received September 19, 1997; accepted May 13, 1998. From the Institute for Neurology and Neurosurgery at Beth Israel North ( R. E. T., M. J. K.), New York Eye and Ear Infirmary ( R. E. T., M. J. K.), New York University School of Medicine ( R. E. T., M. J. K.), New York, New York, U. S. A.; and the Corinthian Diagnostic Center ( L. S.), and the Tennent Institute of Ophthalmology ( D. B.), Glasgow, Scotland. Address correspondence and reprint requests to Mark J. Kupersmith, M. D., Institute for Neurology and Neurosurgery, Beth Israel North, 170 East End Avenue at 87th Street, New York, NY 10128, U. S. A. with mild myopia- related peripapillary pigment changes and a normal nerve fiber layer ( Figs. 1A, IB). The left optic nerve had prominent band optic atrophy with loss of nasal and papillomacular nerve fibers ( Figs. 2A, 2B). Peripapillary pigment changes were present but much less pronounced in the left eye. There were no other ophthalmic abnormalities in either eye. The patient had no other significant medical history. He was born full term, with no known congenital or perinatal infection. He was well developed and neurologically normal. Visual field testing using the Humphrey 30- 2 field analyzer showed the right eye field to be normal ( Fig. 3A). The left eye field had dense temporal macula-splitting hemianopia with partial foveal sparing ( Fig. 3B). The laboratory examination consisting of a hemo-gram, routine serum chemistries, and rapid plasmin rea-gin test produced normal results. Toxoplasmosis, rubella, cytomegalovirus, and herpes ( TORCH) titers were not investigated. Abnormal appearance on computed tomographic scan was limited to a small left optic nerve residing within a formed left optic canal, possibly smaller than the right optic canal. High- resolution gadolinium- enhanced magnetic resonance imaging confirmed atrophy of the left optic nerve from the globe to the chiasm without abnormal signal enhancement. No mass lesion of the optic nerve, orbital apex, optic chiasm, or optic tracts was found ( Figs. 4A, 4B). An area of cortical gray matter heterotopia was noted in the left centrum semiovale ( Fig. 5). DISCUSSION Band optic atrophy is the ophthalmoscopic finding of a horizontal band of optic disc pallor, most often associated with contralateral compressive, traumatic, demy-elinating, and vascular lesions or malformations of the contralateral optic tract ( 1,2). The disc appearance corresponds to atrophy and loss of nerve fibers that enter the disc at its nasal and midtemporal borders. Fibers entering the disc at its nasal border represent the macular temporal eye field, and fibers entering the disc temporally represent the corresponding peripheral temporal eye field. These fibers should cross in the chiasm and project to the contralateral optic tract. The appearance of the disc ip-silateral to the lesion displays a more variable degree of 242 FIG. 1. Color fundus photography ( A) and red- free photography ( B) reveal a tear drop- shaped myopic right optic disc. Mild peripapillary pigment changes are present. Although the photograph is underexposed, direct ophthalmoscopy revealed a normal nerve fiber layer. FIG 2. Photographic technique similar to that used in Figure 1 reveals an atrophic left optic nerve in a band or " bow tie" pattern ( A). Prominent loss of nerve fiber layer is detailed by red- free photography ( B). 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FIG. 4. A: High- resolution gadolinium- enhanced proton density magnetic resonance images failed to reveal a compressive or congenital lesion of the optic tract, chiasm, or retrogeniculate pathway. Note the normal right optic nerve { straight arrowhead) and atrophic left optic nerve ( curved arrow) with formed optic canals ( straight arrows) better seen on coronal computed tomographic imaging. B: The left optic canal may appear smaller than the right canal, but the cuts are slightly off axis, and this appearance may be artifactual. temporal pallor, often pronounced centrally and less pronounced at the disc margin, with variable loss of non-crossed nasal field fibers entering the disc at the superior and inferior arcuate zones ( 1). Band optic atrophy is also present as a component of the syndrome of homonymous hemioptic hypoplasia in which patients have congenital or perinatal damage to a cerebral hemisphere that results in direct damage to or transynaptic degeneration of the ipsilaleral optic radiation, tract, temporal projecting nerve fibers, and contralateral projecting nasal nerve fibers ( 3). Band optic atrophy has not been described in association with focal cortical heterotopia. The current case clearly involved prominent band optic atrophy of the left optic nerve. The functional correlate of loss of nerve fibers corresponding to macular and peripheral temporal eye field is indicated by the dense temporal field deficit. Visual acuity of 20/ 200 in this eye may also have been related to secondary strabismic amblyopia. The right optic disc was horizontally elongated, but the nerve fiber layer was robust. The normal vision, eye field, and robust nerve fiber layer support the contention that the right disc was not atrophic; rather, it was myopic. In fact, the disc area calculation by the Littmann method from fundus photographs reveals the right disc to have had an area of 3.39 mm2 and the left disc an area of 2.71 mm2 ( 4). Both were within normal limits ( normal range, 2.6 ± 0.5 mm2) ( 5). The difference in disc area calculated as 0.68 mm2 was normal and would be found in at least 13% of a normal population ( 6). Although the absence or inconsistency of contralateral atrophic disc .1 Neuro- Ophllialmol, Vol. IS, No. 4. 1998 MONOCULAR BAND OPTIC ATROPHY 245 FIG. 5. Coronal T2- weighted image of cerebral heterotopia ( straight arrows). The lesion extends from the border of the left lateral ventricle to the gray- white matter junction. Note the asymmetrical third ventricles. findings has been described, previous cases showed homonymous field deficits ( 3). The cause of the unilateral band atrophy is unclear. A potential location of a single causative lesion includes posterior intraorbital optic nerve or selective anterior chiasm ( 7). However, we cannot explain how such a selective defect occurred; high resolution imaging did not identify a causative structural lesion of the right optic tract, anterior, or retrogeniculate visual pathway. Furthermore, the absence of bilateral findings suggests the lesion occurred proximal to optic tract. Heterotopia is thought to result from insult to the em-bryologic radial glial fiber system and subsequent interruption of radial migration in the immature brain. Areas of incomplete migration lead to grouped composites of ectopic cells with interrupted synaptic relations. The potential for development of small focal dysplasias occurs even into the perinatal period ( 8). However, the extension of nodular heterotopia from the wall of the left lateral ventricle to surface cortex with normal overlying gyral pattern suggests an early insult, probably within the first 16 weeks of gestation ( 9). Similarly, the optic nerve, chiasm, and tract are formed by the 10th week of gestation and decussations are similar to those of the adult by 13 weeks ( 10). Therefore, a single embryologic insult before the 16th week could have produced cortical heterotopia and band atrophy in this patient. In summary, this case represents a unique example of unilateral band optic atrophy without the typical findings of bilateral disc atrophy and homonymous field defects. In addition, cerebral heterotopia was present, which may serve as a marker of a more global congenital insult that interfered with the normal neural radial migration of the left cerebral cortex and may have contributed to atrophy of the left optic nerve or right optic tract. These associations have not been described in the past. REFERENCES 1. Savino P, Paris M, Sctialz N, Or L. Corbet! J. Optic tracl syndrome. Arch Ophthalmol 1978; 96: 656- 63. 2. Kupersmith MJ, Berenstein A. Neurovascular nearo-ophthalmologx. Berlin: Springer- Verlag, 1994: 301- 5. 3. Hoyt WF, Rios- Monlcncgro EN, Behrens MM, HckelliolT R. I. Homonymous hemioptic hypoplasia. Br J Ophthalmol 1972: 56: 537- 45. 4. Litlmann H. Zur Bcstimmung tier wahren Grosse eines Objckles auf clem Hinlergiimd des lebendcn Auges. Klin Monalsbl Aitgen-heilkd 1982: 180: 286- 9. 5. Jonas JB, Gusek GC. Naumann GOH. Optic disc morphometry in chronic primary open angle glaucoma: I. Morphomctric inlrapap-illary characteristics. Graefes Arch Clin Exp Ophthalmol 1988; 226: 522- 30. 6. Jonas JB, Ticlsch JM, Quigley HA, el al. Race, age, gender, and refractive error- related differences in the normal optic disc. Arch Ophthalmol 1994; I 12: 1068- 76. 7. Unsold R, Hoyt WF. Band atrophy of the oplie nerve. Arch Ophthalmol 1980; 98: 1637- 8. 8. Sarnart HB. Cerebral dysgenesis. New York: Oxford Press, 1992: 263- 4. 9. Barth PG. Disorders of neural migration. ,/ Can Set Neurol 1987; 14: 1- 16. 10. Barber AN, Ronstrom GN, Muelling RJ Jr. Development of ( he visual pathway: optic chiasm. Arch Ophthalmol 1954: 52: 491- 93. ,/ Neiiiv- Ophlhalmot. Vol. M', No. 4. IWH |
