What is the null point in nystagmus?

The null point is the gaze direction where nystagmus intensity is at its minimum and visual acuity is best. Patients with congenital nystagmus often adopt a head turn to position their eyes at this point. Prism in spectacles can shift the null point toward primary gaze, reducing the need for the head turn.

Why do nystagmus patients sometimes see better with contact lenses?

Contact lenses move with the eye, keeping the optical center consistently aligned with the visual axis regardless of eye oscillation. Spectacle lenses remain stationary, so during nystagmus the eye is constantly looking through different zones of the lens, encountering varying amounts of aberration and prismatic effect.

Is nystagmus always a sign of disease?

No. Optokinetic nystagmus (OKN) is a normal physiological response to watching moving objects. End-point nystagmus (a few beats of nystagmus at extreme lateral gaze) is also normal. However, persistent pathological nystagmus, especially if acquired in adulthood, warrants neurological evaluation.

Nystagmus & Eye Movement Disorders for ABO

What Is Nystagmus?

Nystagmus is an involuntary, rhythmic oscillation of the eyes. The movements can be horizontal, vertical, rotary, or a combination. Nystagmus can be present from birth (congenital/infantile) or develop later (acquired), and it may indicate underlying neurological or vestibular conditions.

Types of Nystagmus

Congenital (Infantile) Nystagmus

Present from birth or early infancy. Key features:

Usually horizontal, even in upgaze and downgaze
Often has a null point: a gaze position where the nystagmus is minimal and vision is best
Patient may adopt a head turn or tilt to position the eyes at the null point
Vision may be reduced but is often better than expected given the eye movements
The patient typically does not perceive the world as moving (no oscillopsia)

Acquired Nystagmus

Develops later in life and usually indicates a neurological problem. Unlike congenital nystagmus, acquired nystagmus typically causes oscillopsia (the visual world appears to move or jiggle), which can be very disabling.

Common causes include multiple sclerosis, stroke, brain tumors, vestibular disorders, and medication toxicity.

Optokinetic Nystagmus (OKN)

A normal physiological response to watching a series of moving objects (like telephone poles from a train window). The eyes follow an object (smooth pursuit) then snap back to pick up the next one (saccade). OKN is used clinically to estimate visual acuity in non-verbal patients.

Congenital nystagmus is usually horizontal in all gaze positions, has a null point where vision is best, and the patient does NOT experience oscillopsia. Acquired nystagmus may be in any direction, often causes oscillopsia, and typically requires neurological investigation.

Other Eye Movement Disorders

Disorder	Description	Significance
Cranial nerve palsy	Weakness or paralysis of one or more EOMs	Causes diplopia and limited eye movement
Internuclear ophthalmoplegia (INO)	Impaired adduction on lateral gaze with nystagmus of the abducting eye	Associated with MS in younger patients
Convergence insufficiency	Inability to maintain convergence for near tasks	Causes reading difficulty and eye strain

Optical Considerations for Nystagmus Patients

As an optician, you may serve patients with nystagmus. Key dispensing considerations:

Null point prism: If the patient turns their head to find the null point, prism can be prescribed to shift the null point to primary gaze, reducing the head turn
Contact lenses: May provide better acuity than spectacles because the lens moves with the eye, keeping the optical center aligned
High-quality optics: Aberrations are more noticeable during eye oscillation; aspheric designs and AR coating help
Frame selection: If the patient has a head turn, the frame may need adjustment to accommodate the habitual head position

A child with nystagmus who consistently turns their head to one side is likely positioning their eyes at the null point for best vision. Do not try to "correct" the head turn by adjusting the frame. Instead, mention it to the prescribing doctor, who may prescribe prism to bring the null point to primary gaze.

Assuming all nystagmus means poor vision. Many patients with congenital nystagmus achieve surprisingly good visual acuity (20/30 to 20/60) at their null point. They often function well in daily life despite the visible eye movements. Do not assume they need low vision aids without checking their corrected acuity.

Key Takeaways

Nystagmus is involuntary, rhythmic eye oscillation; congenital or acquired
Congenital nystagmus has a null point where vision is best; no oscillopsia
Acquired nystagmus causes oscillopsia and may indicate neurological disease
Prism can shift the null point to reduce compensatory head turns
Contact lenses may provide better vision than spectacles for nystagmus patients