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Nystagmus

Introduction

Nystagmus is an involuntary, repetitive oscillation of the eyes that can affect vision and balance. It may be physiological or pathological and can result from disorders affecting the central nervous system, vestibular system, or ocular motor pathways. Understanding nystagmus involves exploring its classification, causes, pathophysiology, clinical features, diagnostic methods, and management strategies.

Classification of Nystagmus

Nystagmus is broadly classified into physiological and pathological types.

1. Physiological Nystagmus

Optokinetic nystagmus (OKN): Induced by tracking a moving object, commonly tested using an optokinetic drum.

Vestibular nystagmus: Results from stimulation of the semicircular canals, such as in caloric testing or rotation.

End-gaze nystagmus: Occurs when the eyes are pushed to extreme gaze positions.

Rebound nystagmus: A transient nystagmus occurring when returning from an eccentric position to primary gaze.

2. Pathological Nystagmus

Congenital Nystagmus (Infantile Nystagmus Syndrome - INS): Present from birth or early infancy, typically horizontal, associated with sensory or motor deficits.

Acquired Nystagmus: Develops later in life due to neurological or vestibular disorders.

Spontaneous Nystagmus: Occurs without external stimuli and can be due to brainstem or vestibular dysfunction.

Gaze-Evoked Nystagmus: Appears when the eyes are held in an eccentric position.

Downbeat Nystagmus: Often associated with cervicomedullary lesions.

Upbeat Nystagmus: Linked to brainstem or cerebellar disorders.

Seesaw Nystagmus: Characterized by one eye moving up while the other moves down, seen in parasellar lesions.

Causes of Nystagmus

1. Congenital Causes

Albinism: Abnormal decussation of optic nerve fibers.

Leber’s Congenital Amaurosis (LCA): Retinal dystrophy leading to early-onset nystagmus.

Aniridia: Absent iris associated with foveal hypoplasia.

Achromatopsia: Cone dysfunction leading to sensory nystagmus.

Optic Nerve Hypoplasia: Underdevelopment of the optic nerve.

2. Acquired Causes

Vestibular Disorders: Vestibular neuritis, Meniere’s disease, benign paroxysmal positional vertigo (BPPV).

Neurological Disorders: Multiple sclerosis, stroke, brainstem lesions, cerebellar ataxias.

Drug-Induced Nystagmus: Alcohol, phenytoin, benzodiazepines, lithium, anti-epileptics.

Trauma: Head injury causing brainstem or vestibular dysfunction.

Metabolic Disorders: Vitamin B12 deficiency, thiamine deficiency (Wernicke’s encephalopathy).

Infections: Syphilis, Lyme disease, viral encephalitis.

Pathophysiology

Nystagmus results from an imbalance in the ocular motor system due to:

Disruption in the Vestibulo-Ocular Reflex (VOR): Mismatch between head movement and eye movement signals.

Cerebellar Dysfunction: Involvement of the flocculus, nodulus, or vermis leading to gaze-holding deficits.

Brainstem Abnormalities: Involvement of the paramedian pontine reticular formation (PPRF), medial longiD

1. NYSTAGMUS

2. What is NYSTAGMUS ?

3. Mechanism of NYSTAGMUS

4. Three mechanisms are involved in maintaining foveal centration of an object of interest: Fixation -  in the primary position involves the visual system's ability to detect drift of a foveating image and signal an appropriate corrective eye movement to refoveate the image of regard. The vestibular system is intimately and complexly involved with the oculomotor system The vestibulo -ocular reflex- reflex is a complex system of neural interconnections that maintains foveation of an object during changes in head position.The proprioceptors of the vestibular system are the semicircular canals of the inner ear.The semicircular canals respond to changes in angular acceleration due to head rotatio The neural integrator -A gaze-holding network called the neural integrator generates the signal to convert the eyes from a extreme position to its primary position by tonic contraction of the EOM. The cerebellum, ascending vestibular pathways, and oculomotor nuclei are important components of the neural integrator

5. Pursuit /Saccade Pursuit eye movements allow the eyes to closely follow a moving object. Pursuit differs from the vestibulo -ocular reflex, which only occurs during movements of the head and serves to stabilize gaze on a stationary object Saccades are quick, simultaneous movements of both eyes in the same direction

6. CLASSIFICATION CONGENITAL INFANTILE ACQUIRED PHYSIOLOGICAL PATHOLOGICAL