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Show 278 LETTERS TO THE EDITOR Recurrent Diplopia After Vestibular Nerve Section To the Editor: I am puzzled by a recurring occasional development of diplopia in my patients after vestibular nerve section, and I can find nothing in the literature. Perhaps you or your readers can help. Moreover, my otology co-worker assures me that all otologists are aware of this but simply have not described it in the literature. Because my otologist expects this diplopia, his records are meager, and I must ashamedly admit that my records are not as good as I would like. The facts are these. We section the vestibular nerve or the tentorial half of the eighth cranial nerve, if we cannot see a distinct cleft between the cochlear and vestibular nerves, in the subarachnoid space between the internal auditory canal and the brainstem. This operation has been repopularized by Drs. Norell and Silverstein of Sarasota. Only the gentlest dissection is needed; t~e. c~rebellum is almost never retracted; simply dlvldmg the arachnoid adhesions and removing the spinal fluid will usually give exposure, but sometimes it is necessary to retract the flocculus somewhat. The brainstern is not even touched. In 3.out of our 33 cases the patient developed diploPl~ on gaze to the side opposite from the surgery, ~lth the separation of images always vertical. Testmg these patients is somewhat difficult because they all have nystagmus after the surgery, and they can become confused when asked what it is they are seeing. Nevertheless, it is certain that some do have diplopia. The diplopia seems to be the same on up-gaze as on down-gaze, but at times a red glass test has suggested to me that this was a superior oblique palsy and at other times an inferior oblique palsy. I am wondering if this represents a s~ew deviation, and I have even begun to wonder If the flocculus has something to do with skew deviation, a suspicion which I would have s~of.fed about previously, thinking that a skew devIation must arise somewhere near the midline of the brainstem. Any help you or your readers can offer would be much appreciated. C. Keith Whittaker, M.D. Neurology/Neurosurgery of Kansas City, Inc. 4440 Broadway Kansas City, MO 64111-3373 I Clin Neuro-ophthalmol, Vol. 8, No.4, 1988 Invited Editorial Comment It is important for neuro-ophthalmologists to recognize that patients with peripheral vestibular lesions, i.e., lesions of the labyrinth or of the eighth cranial nerve, can present with ocular symptoms. It is particularly important to recognize these symptoms because, as Dr. Whittaker of Kansas City points out in this issue of the Journal, unilateral selective vestibular neurectomy has been revived for treatment for intractable paroxysmal vertigo. Peripheral vestibular lesions can cause ocular symptoms by disrupting vestibulo-ocular reflexes, the best known of which are the semicircular canal vestibulo-ocular reflexes. These arise from stimulation of the semicircular canals and allow subjects to maintain more or less stable gaze during head rotation by immediately generating ocular rotations in the opposite direction to any head rotations. Acute unilateral lesions of a semicircular canal pair or its nerves cause somatic and visual sensations of rotation, i.e., vertigo (from Latin, vertere to turn), which are similar to sensations we all experience after continuous unidirectional rotation, the somatogyral and the oculogyral illusion (1). Dr. Cogan himself has given a clear account of these sensations from personal experience of a spontaneous attack of acute unilateral vestibular neuritis (2). In contrast, bilateral semicircular canal lesions do no.t caus~ vertigo but rather the syndrome of chromc ves~lbular insufficiency, the chief sympt~~ s o.f whiCh are gait ataxia, particularly when v.lsIOn IS ~estricted, and head movement oscillopsla,. espeCl.al~y ~n the vertical plane (3). Arninogly~ oslde antibIOtics can selectively damage hair cells m the cupula of the semicircular canals, and oscillopsia is perha~s the ~ost common presenting ~~mptom of patients WIth aminoglycoside ototoxiCIty (4). In contrast, vestibulo-ocular reflexes arising from the otoliths are not well known and the symptoms of otolith vestibulo-ocular reflex lesions are not. well rec~gnized: The ocular counterrolling refl~x, l..e., ~onJugate bmocular torsion in the oppOSIte direction to lateral head tilts, is perhaps the be.st known otolith vestibulo-ocular reflex (5) and anses from stimulation of the utricle of the lowermo. st ear. C::0ns~quently, a unilateral peripheral utrIcular leSIon, l.e., a lesion of one utricle or of its nerve, will cause dystonic ocular torsion toward the lesioned side, even with the head erect. This ocular torsio~ is part of the ocular tilt reaction, an oculo-cephalic dystonia consisting of skew devia- LETTERS TO THE EDITOR 279 tion and of head and conjugate ocular torsion toward the hypotropic eye. Westheimer and Blair (6) first used the term to describe a consistent pattern of head and eye posture elicited in the monkey by electrical stimulation of the brainstem. Westheimer and Blair found that stimulation either of the diencephalon or the rostral mesencephalon would cause an ocular tilt reaction toward the stimulated side. We know that an acute unilateral peripheral vestibular lesion will cause a temporary ocular tilt reaction toward the lesioned side (7,8) and that vertical diplopia without any torsional component may be the only symptom of the ocular tilt reaction. The diplopia has no torsional component because the ocular torsion that does occur is the same in each eye. Furthermore, because a normal visual environment contains many redundant clues to verticality, patients with the ocular tilt reaction due to a peripheral vestibular lesion will not be aware of any tilt of the subjective visual vertical. Therefore, those patients who present to ophthalmologists with an ocular tilt reaction due to a unilateral peripheral vestibular lesion will complain only of vertical diplopia. However, because the ocular tilt reaction invariably resolves in the same manner as vertigo and nystagmus, within about 3 weeks by the process of vestibular compensation (8,9), many of the signs may have disappeared by the time the neuro-ophthalmologist sees the patient. Despite this, in most cases, it should not be difficult to make the diagnosis, but two other alternative diagnoses could cause confusion. The first of these alternative diagnoses is an isolated superior oblique paresis, particularly a decompensated long-standing one in which secondary changes have occurred. For example, compare a patient who has leftward ocular tilt reaction due to a left peripheral vestibular lesion with a patient who has a right superior oblique paresis. Both patients will have a left hypotropia and a leftward head tilt, and both patients' vertical deviation will be aggravated by rightward head tilts (i.e., a positive Bielschowsky head tilt test). However, there will be two important differences between the two of them. First, the vertical deviation of the patient with a right superior oblique paresis will be most marked in downward and leftward gaze; in contrast, the vertical deviation of the patient with a left ocular tilt reaction will be most marked in upward and rightward gaze (7). Second, the patient with a right superior oblique paresis will have a torisional component to his deviation, as his right eye will be excyclotorted, whereas his left eye will be straight. In contrast, the patient with a left ocular tilt reac-tion will have no torsional component to his deviation as the ocular torsion is the same in the two eyes. This difference in the torsional components can be demonstrated in two ways: (a) Determination of the torsional angle of the horizontal retinal raphe of each eye with respect to the orbit (8,10) by using an indirect ophthalmoscope (but not by using a direct ophthalmoscope) so that the disc and the macula may be viewed simultaneously. (b) Determination of subjective visual vertical of each by either using Maddox rods, or an illuminated light bar in an otherwise darkened room (11). When using Maddox rods, the patient with the right superior oblique paresis will only rotate the right rod to his right (12), whereas the patient with the left ocular tilt reaction will rotate both rods to his left (13). The second alternative diagnosis to consider is a central ocular tilt reaction. For example, patients with a left lateral medullary lesion involving the vestibular nuclei, i.e., Wallenberg's syndrome, (14,15) and patients with right mesodiencephalic lesions involving the interstitial nucleus of Cajal (16) will also show a leftward ocular tilt reaction. As is usual in neurological diagnosis, the surest way to distinguish between central and peripheral lesions in this case is to find other symptoms or signs of a central lesion and to watch progress. Patients with central ocular tilt reactions will often have other symptoms such as seeing the room upside down, Horner's syndrome, long tract dysfunction, or other cranial nerve pareses. Also peripheral ocular tilt reactions always resolve, whereas central ones may not. Skew deviation by itself is not an accurate localizing sign (17) and careful examination of the subjective visual vertical and of the torsional angle of each in these as in other patients with vertical deviations (12) may reveal that the skew deviation is actually just one component of an ocular tilt reaction. Much more remains to be learned about the effects of vestibular lesions on the visual function. However, careful neuro-ophthalmological evaluation and accurate documentation of patients with vestibular lesions will make an important contribution to this learning process. G. M. Halmagyi W. F. Hoyt Neurology Department RPA Hospital Sydney, Australia Neuro-ophthalmology Unit University of California San Francisco, California , CIin Neuro-ophthalrnol, Vol. 8, No.4, 1988 280 LETTERS TO THE EDITOR REFERENCES 1. Guedry FE. The psychophysics of vestibular sensation. In: Kornhuber HH, ed. Handbook of sensory plzysiology vol. 1, part 2. Berlin: Springer Verlag 1974. 2. Cogan DC. Some objective and subjective observations on the vetibulo-ocular system. Am Ophthalmol 1958;45:74-8. 3. Gresty MA, Hess K, Leech J. Disorders of the vestibuloocular reflex producing oscillopsia and mechanism compensating for loss of labyrinthine function. Braill 1977; 100:693-716. 4. Lerner SA, Metz GJ, Hawkins JE. Aminoglycosideototoxicity. Boston: Little Brown, 1981. 5. Diamond S, Markham C. Ocular counterrolling as an indicator of vestibular otolith function. Neurology (Cleveland) 1983;33:1460-9. 6. Westheimer G, Blair SM. Ocular tilt reaction-a brainstem oculomotor routine. lllvest Ophthalmol 1975;14:833--9. 7. Halrnagyi GM, Gresty MA, Gibson WPR. Ocular tilt reaction with peripheral vestibular lesion. Alln Neural 1979; 6:80-3. 8. Dai MJ, Curthoys IS, Halmagyi GM. Perception of linear acceleration: II. Roll-tilt perception after unilateral vestibular neurectomy. Exp Brain Res (summitted). 9. Cairns H, Brain WR. Aural vertigo: Treatment by division of the eighth nerve. Lallcel 1933;1:946-52. 10. Bixenmann WW, von Noorden GK. Apparent foveal displacement in normal subjects and in cyclotropia. Ophthalmology 1982;89:58-62. 11. Freidmann G. Judgment of the visual vertical and horizontal with peripheral and central vestibular lesions. Brain 1970;93:313-28. 12. Trobe JD. Cyclodeviation in acquired vertical strabismus. Arclz OptlzalnIOI1984;102:717-20. 13. Slavin ML, LoPinto RJ. Isolated environmental tilt associated with lateral medullary compression by dolichoectasia of the vertebral artery. Is there a cause and effect relationship? I Clin Neuro·oplzlhalmol 1987;7:29-33. 14. Hagstrom I, Hornsten G, Silvferskiold BP. Oculostatic and visual phenomena in association with Wallenberg's syndrome. Acta Neurol Scand 1979;445:56&-82. 15. Rapper AH: lIIusion of tilting of the visual environment. A report of five cases. ] Clin Neuro-ophtlzalmoI1983;3:147-5l. 16. Brandt T, Dieterich M. Pathological eye-head coordination in roll: tonic ocular tilt reaction in mesencephalic and medullary lesions. Brain 1987;11O:649~6. 17. Smith JL, David NJ, Klintworth G: Skew deviation. Neurology (Minneapolis) 1964;14:96-105. Author's Reply To the Editor: My head is still reeling after reading the short , Gill Neuro-{)phtlzalmol, Vol. 8, No.4, 1988 treatise by Dr. Halmagyi and Dr. Hoyt. Would diagrams help? Are the authors saying that a "central ocular tilt reaction" is due to disease in the vestibular nuclei in the brainstem? Is the mechanism, therefore, of a peripheral ocular tilt reaction the same as a central ocular tilt reaction, namely, abrupt loss of vestibular function on one side? The nomenclature "ocular tilt reaction" is troublesome to me and I cannot understand whether the diplopia should be on the side named (left or right) or, more precisely, whether the vertical diplopia should be opposite to the lesioned vestibular nerve and vestibular nuclei or ipsilateral. As you can see, I find education painful, but the alternative is even worse! C. Keith Whittaker, M.D. Editorial Comment Applause is in order for Dr. Whittaker's question, the response by Drs. Halmagyi and Hoyt, and also for Dr. Whittaker's subsequent letter. It is obvious that this is not a simple matter. I recommend that neurosurgeons obtain a good neuroophthalmological consultation prior to vestibular nerve section, and then a repeat follow-up examination after that procedure, with careful measurement of the quantitative phorias, Bielschowsky test, and the like, so that this question can be really looked at carefully in a few cases. Would some of you gentle readers also want to write in a few letters to the editor and give us your additional experience and clarification of this question? Thanks for all your help! J. Lawton Smith, M.D. |