Nystagmus in Ophthalmology

Nystagmus

• Nystagmus is a type of involuntary, regular, and rhythmic shaking or oscillating motion of the eyes.
• It can be classified into pendular and jerk types.

Mechanism of Nystagmus

• Nystagmus occurs due to a disturbance in:
  • Visual fixation
  • Vestibular ocular reflex
  • Neuro integration (ocular movement)

Types of Nystagmus

• Pendular nystagmus:
  • Speed of motion of the eyes is the same in all directions
• Jerk nystagmus:
  • Slow and fast phase
  • Eyes move slowly in one direction and then seem to jerk back in the other direction

Characteristics of Nystagmus

• Can be:
  • Unilateral or bilateral
  • Congenital or acquired
  • Horizontal, vertical, or torsional or combined
  • Conjugate or disconjugate
  • Latent or manifest
  • Physiological or pathological

Classification of Nystagmus

• Physiological nystagmus:
  • Found in normal people
  • Not caused by any disease condition
  • Can be used as a diagnostic tool
• Acquired forms of nystagmus:
  • Due to diseases or disorders

Physiological Nystagmus

• Types of physiological nystagmus:
  • Vestibular ocular reflex
  • Optokinetic nystagmus
  • Caloric nystagmus
  • Post-rotatory nystagmus

Vestibulo-ocular Reflex

• A reflexive movement of the eye that keeps the visual image stable on the retina during brief, high-frequency rotation of the head
• Controlled by the vestibular system of the inner ears

Optokinetic Nystagmus

• A physiologic movement of the eyes in response to large, moving visual fields
• Asymmetry of the OKN may suggest lesions of the cerebrum or parietal lobe

Caloric Nystagmus

• A type of VOR (vestibulo-ocular reflex) that is elicited by stimulating the horizontal semicircular canal with either warm or cold water in the ear
• In normal subjects, when cold water is placed in one ear, the eyes will slowly turn toward the ear with the horizontal fast phase away from the ear
• Absence of caloric nystagmus may indicate brain death

Post-rotatory Nystagmus

• A reflexive, transient, conjugate, jerk nystagmus that occurs after the whole body of a subject is passively rotated about the z-axis and then decelerated to rest
• The nystagmus is in the opposite direction of the previous rotation

Early Onset Nystagmus

• Types of early onset nystagmus:
  • Infantile idiopathic or congenital nystagmus
  • Sensory nystagmus
  • Latent nystagmus
  • Spasmus nutans
  • Monocular nystagmus of childhood

Infantile Idiopathic Nystagmus

• Also known as congenital (motor) nystagmus
• Most common type of nystagmus seen in young patients
• Cause is unknown
• Characteristics:
  • Convergence and eye closure dampen
  • Oscillopsia absent
  • Null point present
  • Increases in foveation time and increases the VA
  • Gaze position does not change the horizontal direction of the nystagmus
  • Equal amplitude and fixation in each eye
  • Near acuity is good
  • Inversion of the OKN response
  • Turning of head to achieve null point
  • Abolishes in sleep
  • Latent nystagmus occurs

Sensory Nystagmus

• Caused by abnormalities of the afferent visual system
• Usually seen in 3-4 months olds
• Accompanied by:
  • Achromatopsia
  • Optic nerve hypoplasia
  • Ocular albinism
  • Brain injury

Latent Nystagmus

• Also known as fusion maldevelopment nystagmus
• Benign, early onset conjugate horizontal jerk-nystagmus
• Only manifests after occlusion of one eye
• Characteristics:
  • Direction of the nystagmus is toward the uncovered eye
  • Vision is better binocularly than monocularly
  • Decreases with age
  • Associated with infantile esotropia and dissociated vertical deviation

Spasmus Nutans

• Rare condition with clinical triad of nystagmus
• Onset from 3 to 15 months and disappears between 3 to 4 years of age
• Characteristics:
  • Small amplitude and high frequency of oscillation
  • Usually bilateral
  • Can be unilateral or asymmetrical
  • Caused by chiasmal disorder

Monocular Nystagmus

• Type of nystagmus that involves the same eye at all times in a child
• Causes:
  • Longstanding poor vision in one eye
  • Amblyopia
  • Optic neuropathy
  • Dense cataract
• Can be inhibited by convergence or fixation

Acquired Nystagmus

• Can develop six months after birth
• Usually vertical or torsional
• Causes:
  • Diseases and disorders of the central nervous system
  • Idiopathic nystagmus
  • Metabolic disorders
  • Alcohol
  • Drug toxicity
  • Stroke

Symptoms of Acquired Nystagmus

• Oscillopsia
• Decreased acuity
• Nausea or vomiting
• Vertigo
• Coexisting neurological defect

Types of Acquired Nystagmus

• Nystagmus due to Defective Gaze-holding
• Peripheral Vestibular Nystagmus
• Central Vestibular Nystagmus
• Acquired Pendular Nystagmus

Causes of Nystagmus

• Lack of development of normal eye movement control early in life
• Albinism
• Very high refractive error
• Congenital cataract
• Inflammation of the inner ear
• Medications
• Diseases of the CNS
• Alcohol
• Vertigo

Signs of Nystagmus

• Involuntary eye movement
• Objects may appear blurry and shaky
• Nighttime vision problems or sensitivity to light
• Balance and dizziness

Assessment of Nystagmus

• Check for general ocular health
• Head or ocular trauma
• Birth history
• Present and past medication history
• Systemic health history
• Any associated symptoms

Recording Nystagmus

• Use the mnemonic DWARF
• Direction
• Waveform
• Amplitude
• Reducing direction
• Frequency
• Characteristics