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Show Editorial Comment Optokinetic Nystagmus Strikes Again! In this issul' llf till' Journ'll, Dr. Kj;l1Iman and Dr. Fris~n, llur SWl'dish cllJIt'a~Ul's, have drilwn altentil1l1 ,lgain to the dinicalusl'iulness of optokinetic nystagmus in topical neuro-ophthalmologic diagnosis. In their study of 200 consecutive patients with a solitar\' intracerebral brain tumor, all of whom wert' studied b~' computed tomography, they came to two primar~' conclusions: (a) a homllnynlllus hemianopia does not by itself cause aS~'mmetr~' of the horizontal optokinetic nystagmus responses; and (b) the most likely locations of a lesil1l1 causing both asymmetric optokinetic nystagmus and homonymous visual-field defects are the "upper posterior temporal lobe and the lower parietal lobe." Optokinetic nystagmus has received more clinical neglect than it deserves in recent years. This probably is because most studies of optokinetic nystagmus have been research-oriented electronystagmographic and electro-oculographic recordings using lower animals which have necessitated full-field apparatus, such as placing the animal's head in a large cylinder with moving targets completely surrounding the animal, and the like. There have been suggestions that optokinetic and vestibular nystagmus inputs relay through a common locus in the brain stem; in general, few investigators have emphasized the extremely important clinical uses of optokinetic nystagmus in the office, clinic, and particularly on the neurology ward. Drs. Kjallman and Frisen have utilized a small hand-held optokinetic drum, and I also employ the drum. However, use of an ordinary optokinetic tape is even more practical for ward work. The reader can purchase a nice optokinetic tape, postage paid, by sending a check for $10 to Mrs. Susan Fletcher, 515 Tanglewood Dr., Thomasville, GA 31792, U.S.A. She makes these by hand; they are of excellent quality and extremely convenient to have either in the desk at the office or in your bag when you see patients in hospital consultation. A brief review of the subject as presented by Dr. Alfred Kestenbaum (Clillical mdhods of 1It'/lrlIophthalmologic examinatioll. 2nd ed. New York: 2/5 Grune and Stralton, 1961:189-95) is cited in order to point out that the article in our current issue provides a renewed confirmation of the data that Dr. Kestenbaum presented at that time. Barany studied the behavior of the eyes as they look at a series of moving objects. He turned a large screen with stripes on the inside around the patient, or a drum covered with stripes in front of the patient. Normally, on looking at such moving stripes the eyes are beset by marked nystagmus. The eyes follow one stripe in a relatively slow movement for a certain time and then jump back more or less to their original position. They then follow another stripe, and so on. Thus, nystagmus is generated in which the quick phase is in the direction opposite to that of movement of the stripes. This phenomenon, formerly called railroad nystagmus or train nystagmus, is now called optokinetic nystagmus. Barany found that in some, but not all, cases of homonymous hemianopia, on rotation of the drum in front of the patient's eyes, the optokinetic nystagmus to the side of the hemianopia was missing. For example, in a right homonymous hemianopia, if the drum was turned from the patient's left to the patient's right, the optokinetic nystagmus with rapid phase to the left resulted as expected. However, if the drug was turned to the patient's left, the expected optokinetic nystagmus with rapid phase to the right did not appear. Ohm, however, described two types of hemianopia: (a) cases in which the optokinetic nystagmus to the side of the hemianopia was missing or diminished (Barany's type) and (b) cases in which the optokinetic nystagmus appears normal to both sides in spite of the presence of homonymous hemianopia (Ohm's type). The occurrence of the latter type proved that the originally proposed explanation (absence of the optokinetic nystagmus simply because of the field defect itself) was not sufficient. Kestenbaum found in one of his cases that a tubular field of 10 degrees diameter was preserved, but the optokinetic nystagmus could be elicited promptly to both sides. 2/6 ,. L. SMITH Stt'VI1l'rS l't ,11. and Cords and Strauss found that tht' disturb,lnce of optokinl'tic nystagmus was mllrl' or less ,1SSlKi,ltl'd with ,I certain location of tht' lesion. Thl' sign W,lS found most ottl'n in lesions of thl' 'lIlgUI'H gyrus or supram.uginal gyrus, llr l1l'ighboring p.uts in the ll'mporal and p.uil'tal lobes. Cords studil'd the rl'lationship bl'twl'l'n cl'ntripl'lal ,1Ild Cl'ntrifugal llptic r'ltiitltions. The cortical cl'nlt'r for ct'ntrifug,ll or optomotor fibers was considt'rt'd to surround the visual cortex, primarily at Brodman's Mea 18. They soon join the centripdal bundle in the radiations. It was assumed that the external sagittal stratum of the radiation represented the centripettll bundle, and the internal sagitttli stratum the centrifugal one. The two bundles run together only in the posterior part of the radiation. The most anterior radiations consisted only of the centripetal bundle. The centrifugal bundle ran through the peduncle to midbrain, crossed the midline, and traversed the medial longitudinal fasciculus to the pontine center of conjugate eye movements. Since the sensory and motor fibers were close to each other only in the middle and posterior parts of the radiation, Cords based his hypothesis that optokinetic nystagmus to the side of the hemianopia was absent when the lesion involved both the centrifugal and centripetal fibers. This was the case in a lesion of the middle or posterior parts of the radiation. In spite of the absence of a theoretically satisfactory explanation for the phenomenon, its practical value for topical diagnosis is very high. Kestenbaum defined two types of horizontall1ptokinetic responses. If the response is equal or <llmost equal to both sides (i. e., the normal response), this was called a "negative ON sign" (for optokinetic nystagmus). If the optokinetic nystagmus to the side of the hemianopia was strikingly less than to the opposite side, or completely absent, while the response to the opposite side was present, this was defined as a "positive ON sign." A slight difference between the two sidt's is found occasionally in normal persons, and hence any asymmetry to be considert'd c1inicallv significant (i.e., a positive ON sign) required at kast a 2 + difference. Kestenbaum defined a positive ON sign as llCcurring in three forms: (a) complete absence of both phases of the optokinl'tic nystagmus to the side of the hemianopia; (b) definite weaklll'ss of optokinetic nystagmus to the side of the hemianopia; and (c) absence of only the quick phase, so that an "optokinetic deviation" or an "isolated slow phase" resulted. In spite of their different ap-pearance, and perhaps mechanism, all three ~orrr~s were considered as a "disturbance of optokmehc nystagmus. " Kestenbaum reviewed 59 cases of homonymous hemianopia he personally studied, with the focal lesion substantiated by autopsy, operation, or radiographic findings. In 10 cases of tract and basal ganglia lesions, optokinetic nystagmus (or a positive ON test) was encountered only once, and a negative ON sign was found in the other nine cases. In temporal lobe lesion, the ON test was positive in five and negative in seven. In parietal lobe lesions, the ON sign was positive in all 17 cases. In eight cases involving the occipital cortex, the ON sign was always negative. In two cases where the medullary substance of occipital lobe was involved, Kestenbaum found a positive ON test. He summarized that in cases in which the tract, anterior radiation or the visual cortex was involved, a negative ON sign (normal, symmetrical horizontal responses to both sides) was present. All cases in which the parietal lobe or its neighborhood was concerned showed a positive ON sign. Only lesions of temporal lobe failed to show a uniform behavior. He noted that temporal lobe tumors can interfere with the optic pathways in two \·\,a.vs: the tract may. be im·olved at the base of the brain, or the radiation ma~' be involved in passing through the white matter of the temporal lobe. Among 12 temporal lobe cases, two were basal, three were posterior, and the others could not be located exactly. Neither of the two basal cases showed a definite ON disturbance, and all posterior cases showed a positive ON sign. Kestenbaum concluded that a positive ON sign in homon~'mous hemianopia (completely or essentialh · abl)lished ON to the side of the hemianopia, or absence of its quick phase when ON to the llther side was preserved) indicated that the lesion was in the more posterior white matter or brain, i.e., involved the middle or posterior parts of the optic radiation. A negative ON sign in homonymous hemianopia (equal or almost equal ON to both sides) indicated that the lesion was not in the middle or pl)sterior radiations. The lesion was in tract, lateral geniculate, posterior anterior radiations, or in calcarine cortex itself. He considered the reliability of a positive ON sign was 96%, and the reliability of t~e negative ON sign was 79% if the surroundings ot panetallobe were included. It was 100% reliable as far as parietal lobe itself was involved. One must remember that these findings do not apply to brainstem (infratentorial) lesions, but only to hemispheral (supratentorial) lesions. I like " lZ ... EDITORIAL: OPTOKINETIC NYSTAGMUS 2/7 to teach residents this way. Ii you were being examined on your oral boards, and the examiner took you into a room with 500 patients in it and told you that all of them had homonymous hemianopias and that he was going to give you 2 minutes to differentiate whether these were temporaL parietal, or occipital lobe lesions, the best you could do would be to have all 500 of them stand before you, whip out your trusty optokinetic tape, and pull it to the right and tlwn to the left as they all faced you. You wl)uld promptly find two populations in that room-we might call them the "sheep" and the "gl)ats." The former would have symmetrical optokinetic responses to both sides, and ~'ou would ask them to step to the right side of the room. The latter would have notably and consistently asymmetric horizontal responses, and you would ask them to step to the left side of the room. In a few seconds, the examiner would return and ask how you did. You would say, "Sir, those on the left side of the room (asymmetric responses) are the parietal lobe lesions. Those on the right side (symmetric responses) are the temporal and occipital lobe lesions-and that's the best I could do in the time allotted." I am sure that the examiner would give you a benevolent smile and sign your card! Thanks again to our Swedish friends for re-emphasizing the fact that electrical recording devices are nice, but the clinician with a cloth tape or a hand-held drum still can draw important conclusions in a 30-s objective examination. J. Lawton Smith, M.D. 1011I N"""'·('l'hthnIIlIlJI. Vol. 6. No.4, 1986 |
