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Show Journal of Clinical Nellro- ophthalmology 12( 3): 163- 165, 1992. High Myopia Causing Bilateral Abduction Deficiency Pinar Aydin, M. D., Tulay Kansu, M. D., and Ali Sefik Sanae, M. D. r(;' 1992 Ra yen Press, Ltd., New York We present two cases of degenerative myopia with abduction deficiency. Three mechanisms can explain the defect in the abduction: ( a) the size of the long globe filling the space of the orbits, ( b) the tightness of the medial recti due to long axis of the globe, and ( c) longstanding esotropia becoming decompensated later in life. We believe that high myopia is not a well- known cause of abduction deficiency, and it should be considered in the differential diagnosis. Key Words: Orbit- High myopia- Abduction deficiency- Motility disorders. From the Neuro- Ophthalmology Unit, Institute of Neurological Sciences and Psychiatry ( P. A., T. K.) and the Department of Ophthalmology, School of Medicine ( A. S. S.), Hacettepe University, Ankara, Turkey. Address correspondence and reprint requests to Dr. Pinar Aydin, Bascavus sokak 93- 7, Kucukesat Ankara 06660, Turkey. 163 The commonest etiology underlying bilateral abduction deficiency are sixth nerve palsy and pseudo- sixth nerve palsies. This latter group includes Duane's retraction syndrome, spasm of near reflex, restrictive myopathies such as thyroid eye disease, and myasthenia gravis ( 1). High myopia is not included among the etiological factors. In this report we present two cases with high myopia and limited abduction, and we discuss possible underlying mechanisms. CASE REPORTS Case 1 A 47- year- old woman presented with the complaint of limitation of eye movements, which worsened for the past 2 months. She had no diplopia. On examination visual acuities were 20/ 400 in the right eye and 20/ 200 in the left eye with - 23 (+ 1.00 X 90°), and - 20 ( + 1.00 x 90°) correction, respectively. Color vision was 15/ 15 bilaterally. Ophthalmoscopy revealed bilateral degenerative myopic changes, including peripapillary hypopigmentation and peripheral pigmentary degeneration. Both pupils were isocoric and equally reactive to light. Visual fields with confrontation were full. On primary gaze she was 40 diopters esotropic. She had an abduction deficiency in both eyes ( 90% of normal in 00, and 70% in OS), also her upgaze was slightly limited ( Fig. 1). A Hertel exophthalmometry measurement was 20 mm bilaterally with a base of 122 mm. Her intraocular pressures with applanation were 19 mmHg bilaterally and did not increase with upgaze. Her thyroid tests were normal. An orbital computed tomography ( CT) showed bilateral orbits filled by the globes with no thickening of extraocular muscles ( Fig. 2). Length of the globe was 35 mm 00 and 33.7 mm OS, 164 P. AYDIN ET AL. FIG. 1. Case 1: Deficiency in adduction bilaterally, worse in left eye. measured by axial orbital CT. Tensilon test was negative. She was otherwise healthy and denied any trauma, hypertension, diabetes mellitus, or thyroid disease. She had undergone a strabismus surgery for cosmetic reasons, during which both medial recti were found to be tight. Forced- duction test done at the time of surgery showed bilateral restriction in abduction. A 5- mm recession to medial rectus and 6- mm resection to lateral rectus procedure was carried out to left eye. FIG. 2. Case 1: Orbital computed tomography scan shows both orbits filled by the globes without any thickening of the extraocular muscles. .- '" I'tll,""' ol, Vol. 12, No. 3, 1992 Case 2 A 40- year- old man presented with horizontal diplopia for 20 years. His visual acuities were 201 100 (- 11.0) 00, and 20/ 40 (- 9.0) as. His color vision, intraocular pressure, and visual fields were normal. He had degenerative myopic changes with large posterior staphyloma in his fundi. Both pupils were isocoric and equally reactive to light. Hertel exophthalmometry measured as 19 mm in both eyes with the base of 115 mm. There was no increase in intraocular pressure on attempted upgaze. There was bilateral abduction deficit (. 80% o. f normal) with a left inferior oblique overaction ( FIg. 3). CT scan of the orbit showed globes with right posterior staphyloma, and without thickening of extraocular muscles ( Fig. 4). Length of the globe was 36.7 mm 00,38.5 rom as measur~ d . by axial orbital CT. His thyroid tests w~ re wlthm normal limits. Tensilon test was negative, whereas the forced- duction test revealed restri. ction in abduction. Fresnel prisms were prescnbed for his diplopia. COMMENTS The possibility of bilateral sixth nerve palsy has bee~ ruled out in our case by positive forcedduction test. . ! he m~ st co~ on cause of restrictive gaze defiCIency IS thyrOId eye disease with thick muscle ABDUCTION DEFICIENCY IN HIGH MYOPIA 165 bellies in CT scan ( 2). It has been reported previously that high myopia and endocrine ophthalmopathy may coexist ( 3). We believe that we have excluded this probability as well as myositis with normal extraocular muscle morphology in CT scanning. Three mechanisms can explain the abduction deficiency in our patients with high myopia. The first is that the long globe filling the space of the orbits may cause mechanical limitation in the ocular movements more prominent in adduction as in Case 1. High myopia as a cause of restrictive mo- FIG. 3. Case 2: Bilateral limitation in abduction. .: U. U • l~ I iIlllfl* f. 1l1 FIG. 4. Case 2: Orbital computed tomography scan shows long axis of the globes with no thick extraocular muscles. tility disturbance has been reported previously ( 4). The second mechanism may be the tightness of the medial recti due to long axis of the globe ( N: 23.~ 25.5 mm) causing limitations, especially in the abduction. This can explain the abduction deficiency in both patients. Also, it has been postulated that the medial rectus has abnormal insertion in patients with esotropia and myopia ( 5). Lastly, long- standing esotropia may cause foreshortened medial rectus bilaterally, and esotropia may become decompensated later in life. These two cases suggest that high myopia should be considered in the differential diagnosis of restrictive abduction deficiency. REFERENCES 1. Savino PI. Diplopia and sixth nerve palsies. Semin Neural 1986; 6: 142-- 46. 2. Rootman J. Graves' orbitopathy. In: Diseases of the orbit. Philadelphia: Lippincott, 1988: 241- 80. 3. Ellis FD. Strabismus surgery for endocrine ophthalmopathy. Ophthalmology 1979; 86: 2059- 63. 4. Derner JL, Von Noorden GK. High myopia as an unusual cause of restrictive motility disturbance. Sun' Ophtha/ mol 1989; 33: 281-- 4. 5. Biedner B, Marcus M, Yassur Y. Myopia and congenital esotropia. Ann OphthalmoI1987; 19: 144- 5. I Clill Neuro- ophthalmol, Vol. 12, No. 3, 1992 [CLextraocularmuscle] |
