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Common Threshold Values

Diagnostic Test Abnormality Threshold Clinical Significance
GAZE & SPONTANEOUS NYSTAGMUS
Nystagmus: slow component, followed by fast component. Bilateral gaze nystagmus: eyes open and looking to right or left.
2 Beats (horizontal) in 5 sec. with average velocity of >6 deg/sec.
CNS: nystagmus in all gaze directions or direction changing nystagmus in same gaze direction.
SPONTANEOUS NYSTAGMUS: CNS (brain stem)
PVS: direction-fixed,horizontal, or torsional nystagmus. Inhibited by fixation, follows Alexander's law.* rule out drugs, lack of alertness.
SMOOTH PURSUIT/ TRACKING
Gain: eye velocity/target velocity Asymmetry: right gain – left gain Phase: lag or lead of eye relative to target.
Gain:
Age 50 and under - <70% or >140%
Age 60 – 69 - <65% or > 145%
Age 70 – 79 - <60% or > 150%
Age 80 – 89 - <55% or > 155%
Age 90 and above - <50% or >160%
Gain asymmetry: >30%
Low gain in one direction: CNS lesion. Marked saccadic pursuit:(stair step tracking) CNS lesion
SACCADE TEST
Latency: reaction time in msec. Accuracy: undershoots/overshoots
Velocity: peak eye velocity
Latency:
Age 50 and under - >260 msec
Age 60 – 69 - >270 msec
Age 70 – 79 ->280 msec
Age 80 – 89- >290msec
Age 90 and above – 300 msec
Velocity:
Age 50 and under - <240 deg/sec
Age 60 – 69 - < 230 deg/sec
Age 70-79 - <220 deg/sec
Age 80-89 - < 210 deg/sec
Age 90 and above - <200 deg/sec
Accuracy: <55%
Significant saccadic slowing, overshooting or undershooting:CNS lesion or ocular disorder. Lower velocity of trailing eye:Inter nuclear ophthalmoplegia ( Brain stem)
OPTOKINETIC NYSTAGMUS
Gain: eye velocity/ target velocity.
Gain < 60% is abnormal.
Symmetry > 30% difference is abnormal.
SPV < 6.0 is abnormal
Symmetrical low gain: impaired vision or likely CNS (parietal) lesion.
TORSION W/fix
Normal evoked nystagmus should be observed.
Fixation reduces nystagmus by 50%< 50% Suppression with fixation is abnormal.
If evoked nystagmus is not observed PVS lesion.
Lack of suppression with fixation = CNS lesion.
DIX-HALLPIKE
>2 beats (horizontal) with average velocity >6.0 deg/sec.
• delay onset of nystagmus
• paroxysmal nystagmus
• associated with vertigo fatigable nystagmus
Unilateral: Usually peripheral undermost ear.
Bilateral: peripheral (both ears) or CNS
BPPV: both horizontal and vertical nystagmus (with possible rotation) observed.
POSITIONAL TEST
>2 beats (horizontal) with average velocity >6.0 deg/sec in 5 sec.
• changes direction in a single head position.
• Persists in 3 or more head positions.
• Is intermittent in 4+ head positions.
Eyes open
Direction fixed: usually peripheral.
Direction changing: usually CNS.
Direction changing in single head position: CNS
CALORIC TEST
Directional Preponderance: nystagmus beats stronger one way than another.
Fixation Index: when nystagmus is at its peak, the ratio of velocity with no fixation to velocity with fixation.
Unilateral weakness: of more than 25% is abnormal.
Bilateral weakness: sum of velocities of all 4 irrigations <20 deg/sec.
Directional preponderance: >25% difference.
Caloric weakness: is a function of the labyrinth or Vlll cranial nerve (vestibular portion).
Unilateral: indicates disabled side.
Bilateral: both peripheral organs, acute unilateral lesion or perhaps CNS (cerebellar).
Directional preponderance: is not localizing.
High fixation index: is a prime indicator of CNS.

* THESE COMMENTS ARE GENERALITIES. EXCEPTIONS OCCUR.

Prepared by: PREFERRED PROVIDER CARE, INC. 4/07/05