Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

Jerk nystagmus. This type of nystagmus is biphasic, it has a slow phase in one direction and a rapid phase on the opposite direction. Jerk nystagmus is customarily named after the direction of rapid phase. The slow phase is the fundamental phase, while the rapid phase is a compensatory phase.6 The slow phase is pursuit phase while the rapid phase is saccadic phase.7

Common causes of jerk nystagmus can be congenital or acquired. They are—Opto kinetic nystagmus, end point nystagmus, vestibular nystagmus, defect in fixation, latent nystagmus, congenital jerk nystagmus, gaze paretic.

Mixed nystagmus. This is a rarer than the previous two. In this condition there is pendular nystagmus in primary position and jerk nystagmus in deviated eyes.

Null point (zone) in nystagmus is a point at which the oscillations are either minimal or absent. It is situated mid way between levo version and dextro version. The child tries to keep the eye in such a position that it is nearest to the primary gaze. If the null point falls outside the primary gaze, the child will change the head posture to maintain the gaze in a position that has least oscillation.

Plane of nystagmus can be horizontal (commonest), vertical, torsional, oblique or mixed.

Amplitude. This is a measurement of excrusion of the eyeball in degree during oscillation. It can be fine, medium or coarse. A fine amplitude has an excrusion between 5-15 degrees, excrusion more than 15 degrees is called coarse.

Rate (frequency)8 of nystagmus gives the number of oscillation in a given time. It is roughly divided into rapid and slow. It is given in cycles per second or Hertz, slow is 1-2 Hz, while 5 or more Hz is called rapid or fast.

Relation between amplitude and frequency. Generally the rate varies with amplitude, faster the rate, finer the amplitude and vice versa.3

Intensity of nystagmus is calculated by multiplying amplitude with frequency.

Grades of nystagmus. Alexander’s law states that amplitude of jerk nystagmus is largest in the gaze of the direction of fast component. On the basis of this, nystagmus has been put in to three grades3, 8

First degree. Nystagmus is present only in the direction of fast component. Second degree. Nystagmus present even in primary gaze.

Third degree. Nystagmus is present in both the above two positions.

Classification of nystagmus. Classification of nystagmus is one of the most difficult tasks, because there are about forty types of nystagmus and all of them do not fall in to a simple classification. Some of the useful classifications are :

I.Congenital ; or Acquired

II.As there is overlap of characteristics in many fields, the above classification is not very suitable clinically. The other classification can be

1.Ocular (sensory deprivation) or

2.Non ocular (motor imbalance).

The term ocular nystagmus denotes that the cause is in the eye i.e. macular hypoplasia, macular scar, optic nerve hypoplasia, Leber congenital amaurosia, congenital cataract.

While extra ocular nystagmus is caused by—vestibular, brain stem, cerebellum or spinal cord disorder.9

Ocular nystagmus follows the rule of 2-4-64, which states :

1.If the child has poor vision before 2 years of age, he will always develop nystagmus.

2.Between 2 to 6 years some children will develop nystagmus if central vision is lost. Some will not develop nystagmus.

3.Ocular nystagmus does not develop after 6 years of age with loss of central vision.

Some of the nystagmuses are called physiological. They can be produced artificially by appropriate stimuli, these last only during the presence of the stimulus. They are :

1.Optokinetic nystagmus

2.Rail road nystagmus

3.Evoked vestibular nystagmus

4.Voluntary nystagmus.

The remaining types are put under category of pathological nystagmus. They are sub-divided into :

1.Ocular type of fixation nystagmus

2.Neurological type of fixation nystagmus The former group includes :

1.Congenital jerk nystagmus

2.Hereditary pendular nystagmus

3.Latent nystagmus

4.Latent (manifest latent) nystagmus6

5.Pendular nystagmus of subnormal vision.

6.Spasmus nutans

7.Miner’s nystagmus

8.Acquired unilateral nystagmus The second group consists of :

1.Nystagmus of neurologic origin (brain lesions i.e. chiasma, posterior fossa, brain stem). They are :

(i) Fixational nystagmus (ii) See-saw nystagmus.

2.Defects in gaze mechanism

(i) Gaze paretic nystagmus

(ii) Toxic nystagmus

(iii) Inter nuclear ophthalmoplegia

3. Nystagmus of vestibular defect

(i) Nystagmus of peripheral vestibular disorder (ii) Nystagmus of central vestibular disorder.

A comprehensive classification given by Lyle and Wybar9 is as follows :

1.Ocular fixation nystagmus (a) Physiological

(i) Deviational nytagmus

(ii) Optokinetic nystagmus (iii) Latent nystagmus

(b) Pathological

(i) Blindness

(ii) Defect in central vision (iii) Spasmus nutans

(iv) Miner’s nystagmus

2. Labyrinthine and vestibular nystagmus (i) Labyrinthine

(ii) Lesions of vestibular nerve 3. Nystagmus of central origin

(i) Brain stem lesion (ii) Cerebellar lesion (iii) Spinal lesion

4.Congenital idiopathic

5.Voluntary and hysterical

Symptoms of Nystagmus

1.The child is unaware of nystagmus especially if it is congenital or acquired in early childhood. The parent may observe presence of nystagmus and seek help. There may be history of nystagmus in the family, without any other sign of ocular involvement.

2.Diminished central vision—The vision is poor, there is no correlation between degree of error of refraction and degree of nystagmus. However there may be associated errors of refraction. It is the diminished central vision that is the cause of nystagmus and not the other way.

3.A child may keep the objects very near to see clearly. This induces convergence which in turn reduces nystagmus.

4.Changed head posture—In order to use the null zone, the child may assume abnormal head turn. In vertical nystagmus the child may have abnormal chin position, there may be head tilt.

5.Nystagmic child need not be blind. There should be some vision to develop nystagmus.10

6.Squint—Various types of squint are possible with nystagmus.

7.Other common symptoms consists of photophobia, glare, albinism, achromatopsia.

8.Neurological nystagmus may have symptoms of central nervous involvement i.e. tinitus, hearing loss, vertigo, hemianopia, see-saw nystagmus, head nodding, torticolis.

Diagnosis. Diagnosis of nystagmus is not difficult, large amplitude nystagmus are observed by parents. Important factor in diagnosis is to find out if nystagmus is congenital, acquired in infancy or has developed after six years. Nystagmus developing after six years is of central, vestibular or toxic origin. Fine nystagmus may require examination either by slit lamp or by direct ophthalmoscope.

Various Types of Nystagmus

Physiological nystagmus

1. Optokinetic (opticokinetic)11 nystagmus. This happens when a person gazes at a succession of objects moving past in the field of gaze in one direction. The eye follows one particular object slowly to the limit of comfortable conjugate gaze. After this the object of interest disappears from the field of gaze, the pursuit is given up and the eyes move rapidly to the opposite direction to fix another object of interest and repeat the same. In quick succession resulting in to a jerk nystagmus. The commonest example of this is rail road or train nystagmus. Where a person looking out picks up a part of floating scenario and follows involuntarily till it disappears from the field of gaze and then fixes next object of interest. The fixing movement is towards the direction of the train. The person is not aware of the nystagmus but a person sitting opposite can see the nystagmus.

The same effect can be produced under specific condition by moving an optico kinetic drum (Catford drum) which has alternating white and black strips of same width. The contrast between the white and black strips should be the same all through. When the drum is moved in front of the child, the eyes develop nystagmus, similar to rail road nystagmus and observed by the examiner. Presence of nystagmus means presence of vision, in a child suspected to be blind, absence of opto kinetic nystagmus is diagnostic confirmation of blindness unless the child has serious central nervous system defect including mental deficiency. The other use of opto kinetic drum is to detect malingering as well.

Opto kinetic drum rotated vertically will produce vertical nystagmus.

2. Vestibular evoked nystagmus. This is a jerk nystagmus that can be produced by various methods. Commonly used methods are :

1.Displacement of the endolymph in the semi circular canal.

2.Acceleration and deacceleration of the body.

If cold water is injected in the right ear, a jerk nystagmus will be produced on the left side and irrigation of the ear by warm water will produce nystagmus on the same side, the mnemonic is COWS i.e. cold opposite warm same side.

Pure horizontal nystagmus can be produced by rotating the upright body with head flexed at 30°. A vertical nystagmus can be produced by rotating the upright body in same manner with head tilted towards either shoulder.

3.End point nystagmus. This is ill sustained jerk nystagmus that develops on extreme lateral gaze, when the object of interest is outside the binocular field of vision. It does not occur in vertical gaze. It is more marked in abduction. The nystagmus consists of ten to fifteen beats and occurs on the side of the gaze.

4.Voluntary nystagmus. Some persons can induce pendular nystagmus at will for very brief period, best during convergence. Children learn sooner than adults. Many number of the family may have the skill to produce voluntary nystagmus.

Pathological nystagmus :

1. Latent nystagmus. When both the eyes are open and straight, there is no nystagmus as soon as any of the eyes is covered both the eyes go for jerk nystagmus towards the uncovered eye. The vision in the uncovered eye also diminishes. It is a congenital condition, bilateral, mostly seen in esotropia and in hypertropia. If both eyes are covered the nystagmus disappears. The condition lasts for whole life9.

If the weaker of the two eyes is occluded the nystagmus is finer, the nystagmus is also reduced and vision improved if the eye under observation is adducted.

A nystagmus is termed manifest latent nystagmus when there is manifest nystagmus that becomes more severe if the dominant eye is covered.8

2.Manifest nystagmus. This is that type of nystagmus that is present when both eyes are uncovered and does not increase following covering of either eye. It is bilateral, conjugate mostly horizontal. It may have a mixture of both pendular and jerk nystagmus. These children have better near vision. The nystagmus is reduced on convergence. Generally there is abnormal head posture to bring the eyes in null zone. It disappears during sleep.

3.Nystagmus blockage syndrome. It is common for infantile esotrope children to have either manifest nystagmus or manifest latent nystagmus. On occasions on adduction, the nystagmus is reduced and vision improves. Nystagmus is otherwise present when the eyes are straight. This is called nystagmus blockage syndrome. The nystagmus in primary gaze is horizontal and increases on abduction. They may have cross fixation. They try to see either by converging both eyes or changing the head posture towards the adducted eye.

4.Miner’s nystagmus. Obviously this is not seen in children. This develops in miners after years of work underground in dim illumination. The nystagmus is mostly horizontal but can be oblique as well. It is mostly seen in up gaze.

5.Spasmus nutans3, 12, 13. Spasmus nutans consists a triad of nystagmus, head nodding and troticollis in infants. It’s cause is unknown. It is a benign condition, does not denote any disease, lasts for only a few months and disappears leaving no untoward affect. However sometimes intracranial lesion may produce signs similar to spasmus nutans. The nystagmus is pendular, very fine, rapid. It is horizontal in plane, the nystagmus varies in different gazes. It is asymmetric. The head nodding is not uniform and irregular in rhythm, may be horizontal, vertical or both. Torticollis begins with nystagmus and passes off with it. The condition does not require any treatment.

6.Hereditary pendular nystagmus. It is a congenital nystagmus that may be seen in other members of the family. It lasts for life, horizontal in nature that remains horizontal even on up gaze. However the nystagmus may become jerk nystagmus on lateral gaze.

7.Nystagmus secondary to diminished vision. Clinical presentation is similar to the hereditary pendular nystagmus of congenital origin. The difference is that vision becomes grossly defective in first year of life. The common causes that result in this condition are - congenital optic atrophy, macular lesion, achromatopsia, congenital or developmental cataract, high error of refraction. There is no family history, the condition follows the genetic pattern of the primary cause of defective vision.

8.Congenital jerk nystagmus. There is horizontal jerk nystagmus, which is coarse. The vision is poor but best in null zone. There is abnormal head posture to improve vision.

Some neurological conditions that produce nystagmus

See Saw nystagmus. In contrast to nystagmus described earlier, which were conjugate, this is a disjunct nystagmus. In this as one eye elevates and the other eye depresses. It is often associated with chiasmal lesion producing chiasmal type of field defect.

Down beat nystagmus13. This consists of downwards jerking movements on downwards gaze but can happen in any head posture. Nystagmus increases in amplitude with gaze down and out. It is found in lesions of spinomedullary junction of congenital origin.

Upbeat nystagmus. It may be of congenital origin, drug induced or posterior fossa lesion. In primary position the fast component is upwards.

Management of nystagmus. Management of nystagmus is most frustrating both for the ophthalmologist and the child. Poor vision of nystagmus rarely responds well with optical correction. Medical treatment for oscillation of the eye has limited role in selected cases. Surgical intervention may correct associated squint and reduce oscillation to some extent which in turn increases foveation time and increased distant vision.

Various optical options available are :

1.Prescription of glasses after cycloplegic refraction.

2.Adding concave glasses to distant correction, induces artificial accommodation that is accompanied with secondary convergence. This induced convergence diminishes amplitude and rate of nystagmus thus enhancing vision.

3.Similarly prism may be given to strengthen convergence.

4.Contact lenses have been reported to have reduced amplitude and frequency.

Medical treatment.Many drugs have been used to treat nystagmus. They are - Baclofen, gabapentin, clonazepam, valproate, and carbamazepine.2

Retrobulbar injection of botulin toxin A (Botox) has been found to abolish nystagmus for short period.

Surgical treatment consists of Anderson or Kesten baum procedures. The principle of which is to move the eye to the null zone.

Recession of all the recti have also been advocated.

REFERENCES

1.Lyle T.K. and Wybar K.C. ; Nystagmus in Practical orthoptics in the treatment of squint. First Indian edition. p-592–600, Jay Pee Brothers, New Delhi, 1994.

2.Wheeler D.T. ; Nystagmus in Current ocular therapy. Fifth edition. p-407–410, Edited by Fraunfelder F.T. and Roy H.F. WB Saunders Company, Philadelphia, 2000.

3.Martyn Lois J. ; Nustagmus in Pediatric ophthalmology. Vol. II. Second edition. p-800–807, Edited by Harley R.D. WB Saunders Company, Philadelphia, 1983.

4.Kanski J.J. ; Nystagmus in Clinical ophthalmology. Second edition. p-475–477, Butter worth, London, 1989.

5.Deborah Pavan Langston. ; Nystagmus in Manual of ocular diagnosis and therapy. Third edition. p-323–325, Lippincot Williams and Wilkins, Philadelphia.

6.Rohatgi J.N. ; Nystagmus in Squint basic and clinical aspect. First edition. p-211– 218, CBS Publishers and Distributors, New Delhi, 2003

7.Seal S.K. ; Nystagmus in G.N. Seal’s Text Book of ophthalmology. Fifth edition. p-404–405, Current Book International, Kolkata, 2002.

8.Sharma P. ; Nystagmus in Strabismus simplified. First edition. p-155–163, Modern Publishers, New Delhi, 1999.

9.Lyle T.K. and Wybar K.C. ; Nystagmus in Practical orthoptics in the treatment of squint. First Indian edition. p-595, Jay Pee Brothers, New Delhi, 1994.

10.Reinecke R.D. ; Nystagmus in Ophthalmology secrets. First Indian edition. p-202– 205, Edited by Vander J.F. and Gault J.A. Jay Pee Brothers, New Delhi, 1998.

11.Rosenberg M.A. ; Nystagmus in Principles and practice of ophthalmology. Vol. III, p-1971–1974, Edited by Peyman G.A., Sanders D.R. and Goldberg M.F. First Indian edition. JayPee Brothers, New Delhi, 1987.

12.Glaser J.S. ; Nystagmus and related ocular oscillation in Neuro ophthalmology. p-221-236, Harper and Row Publishers, London, 1978.

13.Gittinger J.W. ; Down beat nystagmus in Manual of clinical problems in ophthalmology. First edition. p-182–184, Edited by Gittenger J.W. and Asdourian G.K. Littlebrown and Co., Boston, 1998.