| OCR Text |
Show Tournai of Clinical Neuro- ophthalmology 10( 2): 100- 102, 1990. © 1990 Raven Press, Ltd., New York Atrophy of Myelinated Nerve Fibers In Pituitary Adenoma Amod Gupta, M. D., Birgit Khandalavala, M. D., R. K. Bansal, M. D., I. S. Jain, FRCS, D. O., and S. P. S. Grewal, M. D. A one- eyed patient was referred as a case of amblyopia secondary to myelinated retinal nerve fibers. Investigations revealed a pituitary adenoma. Following surgical ablation of the tumor, reduction in the myelination became evident. We report this rare occurrence in a case of pituitary tumor with photographic documentation for the first time. Key Words: Myelinated nerve fibers- AmblyopiaField defect- Pituitary adenoma- Demyelination. From the Department of Ophthalmology, Postgraduate Institute of Medical Education & Research, Chandigarh, India. Address correspondence and reprint requests to Dr. Amod Gupta, Department of Ophthalmology, Postgraduate Institute of Mechpl ['.:".-- 1',,"" I'-,"' M, h. Ch. lndigarh 160012, India, 100 Extension of myelination beyond the lamina cirbrosa for a short time after birth results in intraocular myelination ( 1), This occurs as a congenital anomaly in 0.3 to 1.0% of eyes ( 2). Straatsma et al. ( 3) studied both eyes of 3,968 autopsied patients and found myelination of retinal nerve fibers in 37 eyes from 32 patients. Myelination of retinal nerve fibers remains unchanged throughout life unless optic atrophy supervenes ( 1). Only rarely has this phenomenon been documented by fundus photography ( 4- 6), An isolated case of pituitary tumor causing loss of myelination was described in 1905 ( 7). Photographic documentation of atrophy of myelinated retinal nerve fibers in a similar case is presented. CASE REPORT A 30- year- old man was referred with a diagnosis of amblyopia in his left eye secondary to myelinated retinal nerve fibers, He complained of progressive diminution of vision in his left eye for about a month, His right eye was blind since childhood following blunt trauma and showed evidence of healed uveitis and complicated cataract. On examination, his visual acuity was 6/ 60 in the left eye, There was no significant refractive error. Anterior segment examination was unremarkable. Funduscopy revealed characteristic myelination of the nerve fibers along the upper and lower temporal arcades ( Fig. 1). As the visual loss of recent onset and inexplicable, perimetry was advised. This revealed a temporal hemianopic field defect ( Fig, 2). A diagnosis of pituitary tumor was confirmed on computed tomographic ( 0) scan. The patient underwent successful surgical ablation of the pituitary adenoma. A year later, when he was reexamined, his best RETINAL NERVE ATROPHY IN PITUITARY TUMOR 101 FIG. 3. Fundus photograph 1 year following pituitary ablation. The area of myelination along the lower temporal vessels has significantly reduced ( arrow). The borders show linear defects ( small arrows). There is enhanced visibility of the vessels ( arrowhead). ably on this basis that the referring ophthalmologist made a mistaken diagnosis of amblyopia. However, the recent onset and progressive diminution of visual acuity made this assumption suspect and a perimetric assessment was carried out. Field defects of myelinated retinal nerve fibers have been charted if a sufficient number of such fibers are present ( 1). These are typically smaller than the size of myelination would suggest ( 3). Blind spot enlargement occurs when the myelinated nerve fibers involve the optic disc; ring scotoma when the fibers surround the macula and isolated peripheral scotomas are seen corresponding to isolated myelinated nerve fiber patches ( 1). The hemianopic field defect discovered in our patient could not be ascribed to myelination of the retinal nerve fibers, and prompted a diagnosis of pituitary adenoma. Characteristic field defects are seen in 80 to 90% of pituitary adenomas with optic atrophy in 50% of cases ( 8,9). The development of optic atrophy results in decrease in myelination of retinal nerve fibers. The extent of loss may be partial or total ( 4-- 6). Our patient demonstrated subtle linear defects. The early detection and prompt management of the pituitary adenoma probably halted the process of retrograde optic atrophy. Loss or reduction of myelination may be the earliest manifestation of the onset of optic atrophy, particularly in cases where the optic disc is obscured by extensive myelination. III ma corrected visual acuity was 6/ 12. Examination of the fundus disclosed pallor of the optic disc with decrease in myelination of the nerve fibers ( Fig. 3). Repeat CT scan demonstrated an empty sella and perimetry showed no substantial change in the hemianopic field defect. DISCUSSION FIG. 1. The fundus photograph of the left eye at presentation shows myelination of the nerve fibers ( arrow) more marked along the lower temporal vessels. Myelinated nerve fibers do not usually cause reduction in visual acuity. Rarely has extensive myelination of the fundus or involvement of the macula been observed to cause reduction in visual acuity ( 1). Anisometropic myopia, strabismus, and amblyopia have been described in myelination of ipsilateral nerve fibers in the retina ( 8). It was prob- FIG. 2. Visual field chart of the left eye showing temporal hemianopic field defect. I Clin NeuTo- ophthalmol, Vol. 10, No. 2, 1990 102 A. GUPTA ET AL. We suggest that visual impairment in a patient with myelination of the optic nerve fibers should be fully evaluated. Perimetry is useful in such cases and provides diagnostic clues. Photographic documentation is recommended. REFERENCES 1. Miller NR. Clinical neuro- ophthalmology; vol 1. 4th Ed. Baltimore: Williams and Wilkins, 1982: 367- 9. 2. Apple DJ, Rabb MF, Walsh PM. Congenital anomalies of the optic disc. Surv OphthalmoI1982; 27: 3- 41. 3. Straatsma BR, Foos RY, Heckenlively JR, Taylor GN. Myelinated retinal nerve fibres. Am J OphthalmoI1981; 91: 2S- 38. 4. Sharpe JA, Sanders MD. Atrophy of myelinated nerve fibers in the retina in optic neuritis. Br I OphthalmoI1975; 59: 229- 32. 5. Schachat AL, Miller NR. Atrophy of myelinated nerve fibres after acute optic neuropathy. Am J Ophthalmol 1981; 92: 854-- 6. 6. Teich SA. Disappearance of myelinated retinal nerve fibres after a branch retinal artery occlusion. Am J Ophthalmol 1987; 103: 83S- 7. 7. Sachsalber A. Schwund Markhaltiger Nervenfasem in der Netzhaut bei intzundlicher Atrophie des Sehnervem in Folges eines Tumor oerebri. Z. Augenheilkd 1905; 13: 739-- 50. 8. Straastrna R, Heckenlively JR, Foos RY, Shahinian JK. Myelinated nerve fibres associated with ipsilateral myopia, amblyopia and stabismus. Am I OphthalmoI1979; 88: SOf>-- lO. 9. Lyle TK, Clover P. Ocular symptoms and signs in pituitary tumours. Proc R Soc Land [ Med] 1961; 54: 611. |
