NYSTAGMUS (nystagmus; Greek nystagmos a somnolence) — quickly repeating movements of eyeglobes (trembling of eyes). Allocate the following types of N.: vestibular, arising at irritation of receptors of a vestibular mechanism, and optokinetic, appearing at irritation of the visual analyzer (a view of evenly moving objects). Rather seldom also other types of N. meet (professional, inborn, fixating and adjusting, any).
The vestibular nystagmus is important for topical diagnosis and reflects the dynamic changes happening in c. N of page and on the periphery. The N can be investigated at the patient irrespective of weight of a state, even in a coma.
Anatomical structures, with the help to-rykh carry out vestibular N., is neyroepitet ampoules of semicircular channels, the preddverny node, a predoor part of an eighth cranial nerve, vestibular nuclei at the bottom of the IV ventricle crossed (for horizontal N.) and is not crossed - nye for vertical N.) to conduct-buloglazodvigatelnye the ways going in the ascending direction at the bottom of the IV ventricle to kernels oculomotor (VI) and taking away (III) nerves (fig). By means of the weight-tibuloglazodvigatelnykh of the bonds which are taking place in a back longitudinal bunch, vestibular impulses reach eye muscles. In the same way there are reflex combined deviations of eyes therefore the direction of a look does not change at a postural change of the head, N. and compensatory installation of eyes is carried out. Vestibular N.'s mechanism is closely connected with the mechanism of the movement of eyeglobes. This communication is carried out through a complex system of a back longitudinal bunch. A part of its fibers connects system of vestibular nuclei with kernels of the oculomotor and taking-away nerves.
razdrazheniyekhm a vestibular analyzer the movement of an endolymph in semicircular channels is adequate. At the same time there is the whole complex vestibular reactions (see), including vestibular H.
Vestibular N. is subdivided on spontaneous, to-ry is always a sign patol, process on any site of the reflex arc which is carrying out the vestibular N. and which is artificially caused, or experimental, N. revealed by means of caloric test or rotation (see. Vestibulometriya ). Artificially caused N. usually is available and is normal, at pathology its indicators — duration and character change; the pressor N. arising at build-up of pressure of air in outside acoustical pass also belongs to this look.
The spontaneous vestibular nystagmus has the following characteristics: the direction, amplitude, degree, a binoku-lyarnost and a monokulyarnost (the dissociated N.), dominance in a certain direction, the changing character, alternation of phases, a rhythm.
About spontaneous vestibular N.'s direction judge by its bystry phase. It can have various direction: horizontal, vertical, diagonal, rotatorny, converging, mixed (horizontally ротаторное). Horizontal N. meets most often and is observed at defeat of average departments of a rhomboid pole. Vertical N. is usually more weakly expressed, seldom happens isolated, is more often diagonal (horizontal and vertical). Vertical and diagonal N. arise at damage of upper parts of a rhomboid pole, and rotatorny N. — at disturbance in her lower parts. The converging N., at Krom eyeballs move towards each other — a symptom of defeat of a mesencephalon.
Depending on N.'s amplitude divide on small, average and krupnorazmashisty. At small N. the movements of eyeglobes are hardly noticeable and amplitude of their fluctuations is equal to 1 — 2 mm, krupnorazmashisty N.'s amplitude can reach 8 — 10 mm; in rare instances eyeballs move to N.'s time through all palpebral fissure from outside commissure to internal and back. Krupnorazmashisty N. is characteristic of trunk damage of a brain.
Spontaneous vestibular N. depending on the direction of a look, at Krom it appears, divide into three degrees. The nystagmus of the I degree appears only at a look towards a bystry phase H.; The II degrees arises at a direct look; The III degrees takes place at a look towards a slow phase N. Spontaneous vestibular N. usually amplifies at a look towards a bystry phase, and spontaneous N.'s emergence at a direct look and towards a slow phase indicates stronger irritation of a vestibular mechanism.
Usually both eyes (binocular N.) are involved in a nystagmus. Quite often at trunk damages of a vestibular mechanism eyeballs participate in N. not equally: one eye moves with a bigger amplitude, and another — with smaller. In rare instances only one eye takes part in N., and another remains motionless (monocular N.). Monocular N. can be a consequence of defeat of a back longitudinal bunch or kernels of the oculomotor and taking-away nerves.
Quite often spontaneous N. prevails in some direction. N.'s prevalence can be on its degree when N. appears at the smaller angle of assignment of eyes or even at a direct look, and also on amplitude and a tonichiost. More often prevailing is horizontal N., vertical is more rare. Horizontal N.'s prevalence in some direction indicates uneven, asymmetric defeat of labyrinths, roots of the VIII pair of cranial nerves. At acute loss of function of one of labyrinths (purulent labyrinthites, fibrinferments of a labyrinth artery, a crack of a pyramid of a temporal bone) there is spontaneous N. directed towards a healthy labyrinth and disappears in 2 — 3 weeks.
The changing spontaneous N. call a nystagmus of situation or position since it quite often changes or published only in onredelen-ny provisions. So, at a postural change of N. can change amplitude, degree, frequency (most often), the direction or arises only in certain provisions of the patient, or sharply changes the character without change of situation (at tumors of a cerebellum and the IV ventricle).
Spontaneous vestibular To. it consists of rhythmically alternating bystry and slow phases. During a slow phase eyeballs are slowly taken away; at achievement by them the nek-swarm of amplitude of assignment arises a bystry phase H., on an extent a cut eyeballs are returned to the initial position. The normal ratio between bystry and slow phases on duration is usually equal to 1:3, 1: 5. Depending on the nature of alternation of phases H. divide into the following types. Pendulum, trembling, or undulating, N., at Krom slow and bystry phases are identical and the movements of eyes remind the movements of a pendulum, as a rule, is not connected with defeat of vestibular system, and caused by the lowered sight which arose in the early childhood and disturbance of fixing of a look. In rare instances of rough primary trunk defeat (tumors of the bridge, strokes, encephalitis) pendulum trembling N. of vestibular genesis appears.
Clonic tolchkoobrazny N. meets at the compensated form of the central vestibular syndrome arising at defeat of peripheral department of a vestibular analyzer.
Tonic N. is observed at strokes in the acute period, at average and heavy degree of a cherepnomozgovy injury, in an acute stage of trunk encephalitis, in the period of a decompensation of a hypertensive syndrome at tumors of a brain (see. Hypertensive syndrome ).
Sharply expressed N.'s irregularity on amplitude, a rhythm, duration of alternation of phases is characteristic of the expressed trunk defeat (strokes, trunk tumors and encephalitis). Loss of a bystry phase H. when eyeballs during conducting caloric test «departure» towards a slow phase and remain motionless — the terrible symptom characteristic of patients in coma. At deeper coma also slow phase N drops out.
Depending on localization allocate peripheral and central spontaneous vestibular II. Peripheral spontaneous N. arises at damage of a labyrinth or root of the VIII pair of cranial nerves. In the direction this type of spontaneous N. happens horizontally ротаторным, is more rare rotatorny. The vertical, diagonal and converging N. at peripheral defeat do not meet. At death of one of labyrinths spontaneous N. is sent to the healthy party, and at irritation of one of labyrinths — towards the irritated labyrinth. N.'s character rhythmical, with the correct alternation of phases, binocular. It often is followed by increase vestibulovegetativny and the weight-tibulosensornykh of reactions, and also other vestibulosomatichesky reactions (a spontaneous deviation of hands and trunks), at the same time the deviation matches in the direction a slow phase of spontaneous N. Peripheral N. disappears in 2 — 3 weeks in connection with compensatory reorganization in the central departments of a vestibular analyzer.
The central spontaneous N. unlike peripheral is caused by damage of vestibular nuclei and vestibuloglazodvigatelny bonds to system of a back longitudinal bunch. In the direction along with horizontal and rotatorny meet the vertical, diagonal and converging N.; N. dizritmichny, tonichny, monocular becomes frequent. Reaction of a deviation of hands and a trunk at the same time not always corresponds to a slow phase of spontaneous N. (vestibular disharmony). At the expressed central N. patients quite often have no dizziness and ve-stibulovegetativny reactions are not observed. The central N. can remain is very long, sometimes for the rest of life.
For judgment of spontaneous N.'s topic it is necessary to analyze signs of spontaneous vestibular disturbances, these researches of experimental vestibular tests and hearing, and also to consider a wedge, a picture of a disease. Vestibular symptoms, including and vestibular N., are especially accurately shown at acute development patol, process, napr, at acute labyrinthitis (cm)., acute hypostasis of a labyrinth at an attack of a disease of Menyer (see. Menyera disease ), in ostrokhm the period craniocereberal injury (see), stroke (see), subarachnoidal hemorrhages, at quickly accruing hypertensia owing to malignant tumors of a brain. The most often spontaneous N. arises at defeat of a labyrinth and trunk departments of a brain in a back cranial pole (bridge). At tumors of a back cranial pole spontaneous N. meets in 92% of cases, strongly varies in the direction, degree, amplitude, the nature of alternation of phases depending on localization, size, the direction of growth, the nature of a tumor and age of patients. The closer the tumor is located to primary arch of a vestibular reflex (vestibular nuclei, vestibulo-oculomotor bonds in a back longitudinal bunch at the bottom of the IV ventricle), the spontaneous H is expressed more sharply.
So, e.g., at tumors of the bridge spontaneous N. meets in 100% of cases, a mostomozzhechkovy corner — in 95%, the IV ventricle — in 92,7%, a cerebellum — in 84,2% of cases. At tumors of hemicerebrums spontaneous N. meets only in 11 — 12% and is much more weakly expressed, than at tumors of a back cranial pole.
Spontaneous N. often meets at cracks of a pyramid of a temporal bone, in the acute period of any craniocereberal injury, at vascular disorders in vertebralnobazilyarny system, at the trunk encephalitis, arachnoidites and ares-noentsefalitakh which are localized preferential in a back cranial pole at multiple sclerosis.
Usually spontaneous N. is investigated visually (nistagmoskopiya) or registered (nistagmografiya). The method was widely adopted elektronistagmografiya (see), the nystagmus allowing to register precisely.
The research H. is conducted in the following sequence: at a direct look; at extreme assignments of a look; a ducking in the parties and back; in a dorsal decubitus and on one side. Often spontaneous N. especially sharply changes at a ducking in the parties and during the lying of the patient on one side (a nystagmus of situation).
Apply to specification of the diagnosis funkts, loads of a vestibular mechanism, using at the same time colorizing, rotation and a galvanic current.
Artificially caused vestibular nystagmus happens caloric, rotary, postrotary and pressor; the galvanic N is much less often investigated.
Mean the movements of eyeglobes arising at artificial cooling or warming of a labyrinth by caloric N. Heat or cold cause the movement of an eidolimfa in semicircular channels (cold particles fall down, hot rise up), a cut is an adequate irritant of a vestibular analyzer. There are several options of conducting caloric test; the most rational consider injection in outside acoustical pass of 100 ml of t°25 water ° during 10 sec. In case of lack of reaction pour in water with t ° 19 °. With accurate asymmetry of the vestibular reflexes received from both labyrinths pour in 100 ml of hot water (St. 37 °). Normal caloric N. by this technique appears in 25 — 30 sec. and 50 — 70 sec. last. Sometimes normal caloric N. is absent, but there is always accurate a reactive deviation of hands towards a slow phase H. at the closed eyes after colorizing. Caloric test allows to investigate each labyrinth separately. For irritation of the horizontal semicircular channel it is given vertical position for what the head of the patient is thrown back on 60 ° back. At irritation of the horizontal semicircular channel horizontal caloric N. arises a cold water, to-ry it is directed aside, opposite to the studied ear, and at injection of hot water (St. 37 °) there is N. directed towards the studied ear. Caloric N.'s change can be on duration (normal, raised, lowered, lack of reaction) and according to qualitative characteristics, to-rye have the same value that at spontaneous vestibular N.
At peripheral and nuclear defeat of a vestibular analyzer during the colorizing by hot and cool water N.'s expressiveness depends on the studied labyrinth: irrespective of caloric N.'s direction of reaction from a labyrinth will be normal, are raised or reduced. At the subcrustal centers at hot and cold colorizing of N. it will be expressed more in one direction, a thicket towards the center of defeat irrespective of the fact which the labyrinth is irritated. Clear vestibular asymmetries of caloric N. on perife-richesko-core or subcrustal type meet usually in a dekompensirovanny phase of diseases of c. N of page and at defeat of peripheral department of a vestibular analyzer.
Rotary and N.'s postrotator-ny arise in time and after rotation. At the same time at the same time right and left semicircular channels, however, under Evald's law are always irritated, the greatest irritation will be in that semicircular channel where current of an endolymph goes in the direction to an ampoule: this stronger irritation masks irritation from other labyrinth where current of an endolymph goes from an ampoule.
Therefore rotary N. is sent towards rotation, and after and rotary — to the opposite side. Rotation — stronger and short-term irritant, than colorizing. Rotary test is made or in Barani's chair, or at the special vestibular stands with electronic control allowing to dose precisely with the broad ranges angular positive and negative accelerations, speeds of rotation and a stop incentive, to carry out rotation according to the most various programs and objectively to register vestibular reflexes.
At healthy people, and also at unilateral loss of vestibular function N.'s postrotator-ny remains at intensive vestibular irritation. Postrotary N. only at bilateral death of labyrinths or roots of vestibular nerves drops out (bilateral total neuritis of the VIII pair of cranial nerves after meningitis, uses of ototoksichesky antibiotics), and also in a dekompensirovanny phase of diencephalic and subcrustal defeat, but in the latter case vestpbulovegetativny, touch and motor reactions sharply raise. Pressor N. can be caused directly during the pressing by a finger on a trestle. Pressor N.'s emergence indicates existence of destructive process (fistula) in a bone wall of a labyrinth, is more often than the horizontal semicircular channel, owing to hron, a purulent inflammation of a middle ear (see. Otitis ).
Galvanic N. comes under the influence of irritation of a labyrinth direct electric current.
The railroad nystagmus is caused artificially, rotation before eyes of the studied special drum; as well as vestibular, his another has a slow and bystry phase, but a reflex way: the visual irritation from a retina goes through visual pathways to an occipital share of a brain from where the optomotor way begins, to-ry crosses in upper parts of a brainstem at the level of a back cranial pole and comes to an end in vestibular nuclei, and the irritation through system of vestibuloglazodvigatel-ny bonds goes to oculomotor kernels.
Optokinetic N.'s disturbances have important practical value in clinic. At defeat of a peripheral vestibular analyzer optokinetic N. does not change, at emergence of the centers of defeat in a back cranial pole it is directed towards the center of defeat. The centers of defeat in parencephalons cause contralateral loss or horizontal optokinetic N.'s weakening (at localization of the centers of defeat in occipital and temporal areas there is a gomonimny hemianopsia on the party opposite to defeat, and in frontal area — proceeds without hemianopsia).
Other types of a nystagmus. The professional N. of coal miners, miners connected with disturbance of fixing of a look at weak illumination, work in halfbent situation has trembling pendulum character. Due to the improvement of working conditions in mines this pathology meets seldom.
Inborn (hereditary) N. often accompanies other hereditary diseases of a nervous system; it is caused by underdevelopment of vestibular system.
Fixating and adjusting N. arise at healthy people at extreme assignment of a look. Fixating N. longer, adjusting — quickly disappearing. These types of N. are caused by exhaustion of eye muscles at extreme assignment of a look.
Any N. is caused in rare instances of hl. obr. at the persons having potential of reduction and other muscles, not submitting normal to any activity (e.g., the movement by ears).
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