NYSTAGMUS

         

                                             NYSTAGMUS

Definition ;

Involuntary to and fro movements of the eye in  horizontal /vertical or rotary or mixed direction.

Types ; Classified according to the direction of movements :

horizontal           
Vertical               
Rotary                 
Rarer types

Horizontal nystagmus :

Site of the lesion; can be at any one of the following;

1. Retina

2. Vestibular lesions

3. Medullary lesions

4. Cerebellar lesions

5. Medial longtitudinal bundle of the brain stem.

Classification according to the type of movement ;

Pendular

Jerk nystagmus.

Pendular ;amplitutude of the movement is equal in all directions

Jerk Nystagmus : consists of a slow phase and then a fast phase .

-corrective movement. Fast phase determines the direction of nystagmus.

Vertical nystagmus on vertical gaze

Upbeat nystagmus;  fast phase upwards –occurs inmidbrain lesion

Down beat Nystagmus; fast phase downwards; Occurs in medullary lesions.

Rotary nystagmus; occurs in labyrinthine lesions.

Rarer types of nystagmus ;

Sea-saw nystagmus

Occurs in supra sellar lesions .

Intortion or inward movement of one eye and extortion –outward movement of the other eye.

Convergence/retraction nystagmus:

Occurs in midbrain lesion

Physiology of nystagmus; the normal maintenance of ocular posture depends on a) retinal input to the cortex b) labrynthine input

C) Central connections of vestibular nuclei with brainstem and cerebellum.

Hence Nystagmus can be caused by

1.retinal disease

labrynthine disease

Cerebellar disease

Brainstem disease

Examination  for Nystagmus:

Nystagmoid Movement :

 Occurs normally at extreme of gaze fixation.

True Nystagmus ;to test eyes should deviate just 30°from midline.

Fig   

Degree of nystagmus;

I degree- with eyes deviated to only one side.

II degree: With gaze to one side andin midline also.

III degree; With eyes in any direction

I.Retinal or ocular nystagmus:

                                                                                                                  

Physiological                 Pathological (Ocular nystagmus)

Optokinetic                   In cases with defective vision

 

                                        1.Pendular

                                        2.Rapid

                                        3.Persistant thr’ lifetime

                                        4. Intensifies while looking to side

                                   Causes;

                                   Albinism

                                   Congenital cataract

                                   Congenital macular defect

II. vestibular Nystagmus :

Can arise from natural stimulation of vestibular apparatus

Damage to the vestibular apparatus can cause imbalance between 2 sides.So drift to damaged side and fast compensatory movement to opposite side.

Physiological vestibular nystagmus can be caused by  caloric test.

Pathological by damage to vestibular apparatus or vestibular nuclei.

Fig ;

III .Labrynthine nystagmus ;e.g. Miniers disease ,vestibular neuronitis

1. Slow phase to the side of the lesion
2. Fast phase to normal side
3. In severe cases III degree nystagmus
4. nysagmus intensifies if eye turned to opposite side.
5.  Vertigo can accompany.

IV.  Positional Nystagmus:another form of labrynthine nystagmus

Occurs when patient assumes acertain posture.

To elicit : suddenly reposition the patient from lying to sitting posture or viceversa.

1.   occurs after a delay of seconds

2.   Often rotary

3.   but fatigues on repeated testing .

V. C.N.S. nystagmus

Damage to central  connections of  vestibular nerve

1.Vestibular nuclei in the medulla

2.Brainstem

3.Cerebellum.

C.N.S nystagmus   :  horizontal

                                 Vertical

                                 Dissociated (unilateral only)

1. Direction of fast phase is determined by direction of gaze(multidirectional)
2. Vertigo absent
3. Signs of other nuclei or tract involment in brain stem.

Etiology :

Vascular,demyelinating,tumor,¶Wernicke,s, alcoholic,nutritional,eptoin

   Cerebellar Nystagmus:

 Features: Quick phase to the side of the lesion (as opposed to Labrynthine)

Rebound Nystagmus;

When eyes overshoot on returning to resting position in midline.

Posterion fossa Lesions ;

 This can cause positional nystagmus.D.D:Labrynthine disease.

1.   Absence of delay before onset

2.   2.No fatigue on repeated testing.

3.    Can occur with any  head movement.,not just in one position.

VI. Internuclear ophthalmoplegia (Ataxic Nystagmus)

M.L.F Lesion.

¶MLF Connects 3rd and 6^th nerve nuclei to opposite side nuclei so that coordination of eye movement occurs normally.

Hence MLF lesion causes dissociated nystagmus;i.e. eyes no longer move as one. So there is nystagmus in one eye, not in other.

Features: ✣Failure of adduction (3^rd nerve nucleus is mainly affected)

✣Nyastagmus in the abducted eye.

In Unilateral MLF lesion eye fails to adduct to affected side.

Differential; bilateral 3^rd nerve lesion .

✿ Pupils not affected✿When eyes are tested individually for movements some adducton occurs.

Fig

VII.Congenital Nystagmus:

❊Present from birth.

❊Family history may be present

❊It is important to recognize this so that unnecessary investigations are –avoided.

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