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Show Journal of Neuro- Ophthalmohgy 20( 3): 163- 165, 2000. © 2000 Lippincott Williams & Wiikins, Inc., Philadelphia Short Communication A Case of Superior Oblique Myokymia Observed by an Image- analysis System Yuuki Hayakawa, MD, Mineo Takagi, MD, PhD, Hiruma Hasebe, MD, PhD, Shigeru Hasegawa, MD, PhD, Ritsuko Takada, MD, PhD, Tomoaki Usui, MD, PhD, Haruki Abe, MD, PhD, Kikuo Shibasaki, MD, Hiroshi Yaoeda, MD, PhD, Kazuhiko Ukai, PhD, and Norio Ishikawa Superior oblique myokymia is a microtremor of the eye that causes monocular torsional oscillopsia. A modified Harada- Ito procedure was used to treat a case of the disease in a 20- year-old woman. The authors used video- image analysis pre- and postoperatively to evaluate the effect of the surgery on abnormal torsional eye movements. This analysis revealed that before surgery, the abnormal torsional movement had a very regular cycle ( duration of attack, 8.0 ± 0.5 s; time interval between attacks, 18.7 ± 3.2 s; n = 9). After the surgery, amplitude of the abnormal torsional eye movement was reduced, and the oscillopsia had subjectively improved, although the movement cycle remained unchanged. The authors' video- image analysis, which used iris striation, proved to be a useful method for clinical measurement of torsional eye movements. Key Words: Modified Harada- Ito procedure- Ocular torsion- Superior oblique myokymia- Video- image analysis. Superior oblique ( SO) myokymia is a microtremor of the eye caused by abnormal involuntarily contraction of the SO muscle. We measured the ocular torsion of SO myokymia using a newly developed video image-analysis system ( 1) before and after surgery. A 20- year- old woman had experienced oscillopsia OD for 4 years. The patient's medical history and familial history were unremarkable. There were spasmodic combined downward and intorsional movements OD. The Supported by the Medical Social System Foundation, Tokyo, Japan. Manuscript received July 15, 1999; accepted May 18, 2000. From the Department of Ophthalmology ( YH, MT, HH, SH, RT, TU, HA), Niigata University School of Medicine, Niigata, Japan; the Seirei Hamamatsu General Hospital ( KS), Hamamatsu, Japan; the Yaoeda Eye Clinic ( HY), Nagaoka, Japan; the Faculty of Social and Information Sciences, Nihon Fukushi University ( KU), Handa, Japan; and Nihon Kohden Corporation ( NI), Tsurugashima, Japan. Address correspondence and reprint requests to Yuuki Hayakawa, MD, Department of Ophthalmology, Niigata University School of Medicine, 1 Asahimachi, Niigata, 951- 8510 Japan. downward movements increased when the eye was in the inferior medial position, and the torsional movements became prominent when the eye was in the lateral position. No abnormal eye movement was observed OS. No vascular compression of the trochlear nerve, lesions in the cerebellum or brain stem, or abnormalities of the eye muscles were seen on magnetic resonance imaging scans. The recording system had a combined set of two small charge coupled device cameras and two infrared reflecting dichronic mirrors and light emitting diodes for illumination of the iris ( 2). Dynamic images of the iris were recorded by a digital video recorder and replayed and captured on a personal computer using a digital video capturing board ( Radius Moto DV, Mountain View, CA). The captured movie was analyzed using Wayne Rasband National Institutes of Health Image 1.6 ( Research Services Branch of the National Institute of Mental Health, Bethesda, MD). The polar cross- correlation method using iris striation was used for calculating torsional eye movements. Macro code and PASCAL code were used for this purpose. The torsional movement of the eye along the axis of the pupillary center was calculated every Vw s with a resolution of 0.2°. After the analysis, we found a very regular cycle in abnormal torsional movement. There was a tonic large intorsional eye movement with an amplitude of 10- 11° ( jerk) ( duration of attack, 8.0 ± 0.5 s; interval between attacks, 18.7 ± 3.2 s; n = 9), which was damped slightly and was associated with torsional high frequency tremor ( oscillation) with an amplitude of 1 to 2° ( Fig. 1). The amplitude was extraordinarily large compared with previous reports of data that ranged from 0.5 to 1.5° ( Table 1) ( 3- 7). Between attacks, there was no torsional tremor. The patient had been administered carbamazepine ( 200 mg/ d), followed by clonazepam ( 2 mg/ d), but this 163 164 Y. HA YAKA WA ET Ah. 15 10 deg pre- operative / x Hk> M, x r^ v\ A^ j\ ffK,^ Mi *_ U|| J* J-^ A. - 5 20 40 60 80 100 120 140 / \ L^ w- T * ? ^ ^ \ j-"- « v 60 80 100 120 U 0 FIG. 1. Abnormal torsional eye movement OD. The upper panel shows preoperative recording, and the lower panel shows postoperative recording. The ordinates indicate the amplitude (°) of ocular torsion and the abscissas indicate the time ( s). The upper deflection indicates intorsion. The large vertical noise was caused by blinking. The postoperative amplitude was smaller than the preoperative amplitude. Note the very regular cycles of the torsional eye movements. TABLE 1. Past recording findings of superior oblique myokymia Reference Hoyt and Keane, 1970 ( 3) Ishikawa, 1995 ( 4) Morrow et al, 1990 ( 5) Leigh et al., 1991 ( 6) Thurston and Saul, 1991 ( 7) Amplitude 1- 1.5° 1.5° 1° Jerk Duration 3- 5 s 2- 3 s 10 s 0.5 s Amplitude 1- 2° > 1° 0.3- 1.7° Oscillation Frequency 12- 15 Hz 10 Hz up to 20 Hz up to 50 Hz Unknown Recording method Video recording Unknown Search coil Search coil Search coil FIG. 2. Operative procedure ( modified Harada- lto procedure). The right eye is seen from above. The anterior attachment of the superior oblique was cut to a width of 7 mm and sutured onto the sclera 15 mm posterior to the corneal limb and 3.5 mm in from of the medial rectus muscle. J Neuro- Ophthalmol, Vol. 20, No. 3, 2000 IMAGE ANALYSIS OF SUPERIOR OBLIQUE MYOKYMIA 165 treatment was not effective. We performed a modified Harada- Ito procedure ( 8) OD. The superior rectus muscle was cut to obtain a good operative field. The anterior attachment of the SO muscle was cut and then sutured onto the sclera in order to weaken the torsional effect of the muscle ( Fig. 2). Because the patient was not experiencing pain, we operated with local- anesthesia eye drops; we were therefore readily able to confirm the degree of resection needed. The continuous vibration of the SO muscle could be felt when the muscle was grasped. After the surgery, the torsional oscillopsia was subjectively improved when the eye was in the primary position, probably because it was within the range of sensory cyclofusion. Palsy or paresis of the SO muscle was not found on the Hess chart. The eye movement was recorded again 95 days after surgery. The amplitude of the jerk had decreased to 6 to 7°. The cycle was still regular after the surgery ( duration of attack, 7.5 ± 0.3 s; interval between attacks, 19.3 ± 3.2 s; n = 9). The cause of SO myokymia is still unknown. There have been many suggested causes of SO myokymia, such as nuclear disorder ( 3), lesion in the dorsal cerebellar flocculus ( 4), postdenervation phenomenon peculiar to the SO muscle ( 9), or supranuclear control of the pathologic unit triggered by a viral infection ( 10). However, because the torsional movement in the current case had a very regular cycle, it could have originated from a supranuclear disorder. It was beneficial to analyze the torsional eye movement using this video image- analysis system because an extraordinarily large amplitude of torsion ( jerk) was measured accurately, and the effect of surgery could be objectively assessed, and because the characteristic regular cycle, which was not noticed during examination, was clearly shown. This method would be useful to measure clinically the low- frequency component of abnormal eye movement with a torsional component. REFERENCES 1. Ukai K, Saida, S, Ishikawa N. Measuring torsional eye movement of head mounted display users. Jpn J Ophthalmol 2000 ( in press). 2. Ishikawa N, Kobayashi N, Hosaka H, et al. Development of a new examination system for vertigo. Three dimensional analysis of eye movements by an iris striation tracking method. Jpn J Med Electronic Biological Engineering 1995; 33: 192- 202. 3. Hoyt WF, Keane JR. Superior oblique myokymia. Report and discussion of five cases of benign intermittent and ocular mi-crotremor. Arch Ophthalmol 1970; 84: 461- 7. 4. Ishikawa H. Mechanism of superior oblique myokymia. Equilibrium Res 1983; 42: 59- 61. 5. Morrow MJ, Sharpe JA, Ranalli PJ. Superior oblique myokymia associated with a posterior fossa tumor. Oculographic correlation with an idiopathic case. Neurology 1990; 40: 367- 70. 6. Leigh RJ, Tomsak RL, Seidman SH, et al. Superior oblique myokymia. Quantitative characteristics of the eye movements in three patients. Arch Ophthalmol 1991; 109: 1710- 3. 7. Thurston SE, Saul RF. Superior oblique myokymia. Quantitative description of the eye movement. Neulology 1991; 41: 1679- 81. 8. Kosmorsky GS, Ellis BD, Fogt N, et al. The treatment of superior oblique myokymia utilizing the Harada- Ito procedure. J Clin Neuro- ophthalmol 1995; 15: 142- 6. 9. Lee JP. Superior oblique myokymia. A possible etiologic factor. Arch Ophthalmol 1984; 102: 1178- 9. 10. Kommerell G, Schaubele G. Superior oblique myokymia. An elec-tromyographical analysis. 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