20. Investigation and management of nystagmus in optometric practice

What is nystagmus?

constant, involuntary, oscillation of the eyes

3 categories of nystagmus?

Physiological nystagmus, Early-onset nystagmus, Acquired nystagmus

describe the 2 components of nystagmus

1. slow phase drift away from the assumed position of gaze

2. fast phase that returns the eyes to the position of gaze

What is Optokinetic nystagmus (OKN)

an oculomotor response to minimise retinal slip provoked by large moving stimuli or the entire visual field

What is end point nystagmus?

End-point nystagmus is seen when looking at extreme positions of gaze

3 types of early-onset nystagmus

• latent

• spasmus nutans

• infantile

Features of Early-onset nystagmus

Nystagmus that presents within the first few months of life • Unless it results from a condition that has caused an acquired nystagmus such as a head trauma or brain injury

define Latent nystagmus (early-onset nystagmus)

Form of nystagmus that appears when one eye is occluded (latent-latent nystagmus) or worsens upon occlusion (manifest-latent nystagmus)

what is the beat direction in latent nystagmus

• In latent nystagmus the beat direction of the nystagmus is always towards the fixating eye

• For instance, if the right eye is occluded both eyes will beat to the left (fixating eye; left-beating nystagmus)

• Switching the occlusion to the other eye will reverse the beat direction

What is latent nystagmus also known as?

fusion maldevelopment nystagmus syndrome

define Spasmus nutants (early-onset nystagmus)

a high frequency, low amplitude nystagmus of disconjugate nature with irregular head nodding and abnormal head posture

Onset of spasmus nutants

Onset during the first year of life

does spasmus nutants resolve?

the condition tends to resolve spontaneously usually within two years of onset•

define infantile nystagmus (early-onset nystagmus)

a constant nystagmus, usually predominantly in the horizontal axis, of similar amplitude in each eye, and at an average frequency of 2-3Hz (Vertical and torsional (rotary) components may also be present)

How does infatile nystagmus prsent?

Develops in the first 6 months of age and persists throughout life

What is the waveform

the pattern of eye movements (eye position change between beat-to-beat) seen in each individual

How does the waveform vary?

between individuals, and often, within the same individual at different times of gaze angles

Classification pf nystagmus waveform?

jerk or pendular

What is Jerk nystagmus?

the waveform has a slow phase or drift away from fixation, which is the abnormal movement, and a fast corrective movement (saccade) in the opposite direction

What is Pendular nystagmus

the waveform is characterised by equal velocity slow phase movements in both directions similar to the motion of a pendulum

3 ways to describe a waveform

• amplitude

• frequency

• foveation period

What does the amplitude of a nystagmus waveform represent

Amplitude: measured in degrees, represents the extent of the movement between the start of the drift away from the fixation and the start of the corrective fast movement (saccade) in the opposite direction

What does the frequency of a nystagmus waveform represent?

Frequency: number of beats that occur in a given time. The greater the number of beats, the higher the frequency (i.e. low, moderate or high)-

What does the foveation period of a nystagums waveorm represent?

Foveation period: area in the waveform where the eye velocity is at a minimum and VA is maximal (where the image has returned to the fovea before it drifts off again)

What is used to describe typical nystagmus waveform?

Amplitude, Frequency, Foveation period

What is the null zone

The null zone is the gaze angle at which the nystagmus is minimised

Infantile nystagmus null zone

73% of individuals with IN have a null zone within the 10 of primary gaze position • Most of these individuals use a precise head posture to facilitate this, particularly if the null point is more than 20 outside of the primary position• In around 44% of individuals with IN, convergence also reduces the nystagmus•

How is the nystagmus null zone and VA related?

Although there is controversy in relation to the null zone and an improvement of VA, patients with nystagmus often report that vision is at least 'most comfortable' in this position

What is Oscillopsia

the perception of the world as moving back and forth

Who is more likely to experience oscillopsia

Patients with acquired nystagmus are much more likely to experience oscillopsia

head shaking of infantile nystagmus

Some individuals with IN also exhibit regular head oscillations that increase in intensity with effort to see

Infantile nystagmus and refractive error and astig

• High refractive error is common in IN

• A broad range of refractive errors may be found

• Tendency towards myopia

• High incidence of corneal with-the-rule astigmatism

• Astigmatism seems to increase with age

define Idiopathic infantile nystagmus and what testing is used

Idiopathic IN is a diagnosis by exclusion where all other possible causes and associated conditions have been ruled out

• Electrophysiological testing is essential to rule out some of the conditions known to be associated with IN

What is Acquired nystagmus

Pathological nystagmus may develop as a result of disease, injury often to the vestibular or central nervous system

Common causes of acquired nystagmus?

multiple sclerosis and stroke

When should nystagmus be reffered?

Any suspicion of acquired nystagmus should result in a prompt referral • Every patient with any form of pathological nystagmus should have (or have had) a thorough neuro-ophthalmological examination • Any patient presenting for the first time with nystagmus requires urgent referral to rule out life-threatening causes

Features that should raise the suspicion of acquired nystagmus

• Asymmetry, that is disconjugacy of the nystagmus eye movements

• Significant vertical component

• Reports of oscillopsia

Key Qs for H&S with nystagmus

1. How long has nystagmus been present?

2. Is oscillopsia perceived?

3. Is there a history of strabismus?

4. Is there a family history of nystagmus?

What should be assessed with nystagmus during optometric exam?

• Whether the nystagmus intensity increases with occlusion

• Whether the eye movement is symmetrical

• Whether the beat direction changes depending on which eye is covered

• Whether head shaking is present

• Whether convergence reduces the nystagmus

• Whether there is a null zone and whether a head posture is used

What modifications can allow an accurate refraction for px with nystagmus?

• Avoid phoropters

• Allow patients to use their preferred head position to use their null zone

• Use wide aperture trial lenses

• Give patients plenty of time to respond to letters when reading the chart

• Use fogging lenses and conduct a binocular refraction instead of occlusion

• VF may be performed in patients with nystagmus nut the results may not be very sensitive to small field defects

• CT may be more difficult due to the constant movement of the eyes

3 steps in an 'ideal' management plan for patients with nystagmus

1. Treat the underlying condition (if any)

2. Fully correct the refractive error

3. Minimise the nystagmus intensity

What is Nystagmus Network

a national charity an support group that can provide individuals with nystagmus and their families with practical information

Management of latent nystagmus

• Refractive error correction for accommodative SOT and/or surgical management alignment of the deviation can reduce the nystagmus intensity

• These interventions can convert the manifest-latent nystagmus to latent-latent nystagmus and improve binocular VA

what special considerations should be taken when managing an amblyopia associated or combined with a latent nystagmus

The nystagmus will worsen with traditional occlusion (patching) so use penalisation or atropine therapy should be used instead

Management of infantile nystagmus

At present there is no effective treatment for IN but there are a number of interventions

• Optical management

• Recommendations regarding the use of the null zone

• Surgical management

• Pharmacological management

management of infantile nystagmus

• Full refractive error correction should be given

• CL

• Prism therapy to modify the null zone

why are Contact lenses good for infantile nystagmus?

CL provide superior refractive error correction over spectacles in nystagmus due to the reduction in peripheral lens aberrations and lack of prismatic effect when the eye moves away from primary position

Some studies report that CL provide at least a line of VA improvement compared to spectacles

What is Prism therapy to modify the null zone for IN

Prisms may be used to allow patients to adopt their null zone of gaze while keeping the head straight • For example, a patient with a null zone right-gaze will turn the head to the left and would benefit from 'base left' prisms in front of each eye (BOUT in LE and BIN in RE)

Prism therapy options to modify the null zone

An alternative is to use Fresnel stick-on prisms, although neither option may be cosmetically acceptable to the patient

Many nystagmus have a convergence null zone and therefore it is possible to reduce the nystagmus intensity by inducing convergence with prisms BOUT

Rarely the null zone is in divergent position, in which case BIN prism to induce divergence can reduce the nystagmus intensity

Recommendations regarding the use of the null zone in infantile nystagmus

• Using the null zone of gaze usually improves visual function in IN

• Individuals with nystagmus often adopt an abnormal head posture to achieve the required gaze position

• While such head posture should not be dissuaded, long-term use of such head posture may lead to a restriction of neck movement

• Besides using prisms, adjustment to the surroundings, such as changing the seating position during viewing, can be made to place the eyes into the null zone while keeping the head straight

how to manage aquired nystagmus

same as IN

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