Interpretation of VNG/ENG

Spontaneous nystagmus criteria

Anything 3 degrees or less is not significant

4-5 is noteworthy

6 or greater is clinically significant

Why must we know if there is spontaneous nystagmus in reclined position

Need to know if there is nystagmus for when we do calorics because it is in the same position

Gaze abnormalities are peripheral or central?

Both

Follow Alexander’s Law to know if it’s peripheral

Saccadic abnormalities likely of what origin?

Central

Saccadic parameters to look at

Latency

Velocity

Accuracy

Gain for smooth pursuit

eye velocity / target velocity

Symmetry vs Asymmetry during smooth pursuit

Symmetry - person can track target as it moves both ways

Asymm - Eyes can move when target moving to the right but when moving to the left they have saccadic movements

Test used for BPPV

Dix-Hallpike

Signs of BPPV (posterior canal)

Delay in nystagmus when going from seated to supine

Should see torsional or rotary nystagmus

Nystagmus should fatigue usually within 20 seconds

Sitting up should make the nystagmus go in opposite direction

Do you want to try to suppress nystagmus during positional testing?

Yes

What is considered significant nystagmus during positionals

6 degrees per second - clinically significant

4-5 - noteworthy

3 or less - insignificant (unless it supports other test findings)

What are we measuring during caloric testing

Degree of nystagmus

What is considered significant difference during calorics

20%

Fixation index

SPV with fixation / SPV without fixation

Abnormal fixation index

50% or greater

Abnormal fixation index is indicative of what

Central issue (the person is unable to suppress nystagmus)

Bilateral weakness

Less than 6 SPV is abnormal

All 4 irrigations did not create SPV of 6 d/sec

Unilateral weakness

20-25% difference between ears

One side weaker than the other

Directional preponderance

Comparing LB vs RB nystagmus

Non localizing finding

Positive number = L weaker

Negative number = R weaker

Can calorics localize side of lesion?

Yes

Does a bilateral weakness indicate complete loss of vestibular function?

No

Can calorics be the only abnormal result from a comprehensive exam?

Yes

Testing very low frequency