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optokinetic nystagmus test gain interpretation normal values
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OKN gain normal values interpretation asymmetry
Here is my full evaluation of the two Optokinetic Test (OKN) printouts.
Optokinetic Nystagmus (OKN) Test - Evaluation
Patient ID: CCDA00274 | Date: 29-May-2026
What the Test Measures
The OKN test uses a moving visual scene (stripes or patterns) and records the eye's tracking response. Two key parameters are reported:
- Gain = slow-phase eye velocity / stimulus velocity. Normal is close to 1.0 (typically 0.8-1.0+). A gain near 1.0 means the eyes are tracking the stimulus accurately.
- Fast Phase Direction = the direction of the corrective quick beats (saccadic resets).
Page 1 - Top to Bottom 10°
| Parameter | Right Eye | Left Eye |
|---|---|---|
| Vertical Gain | 1.02 | 0.93 |
| Fast Phase Direction | 108.24° | 121.48° |
Interpretation:
- Both gains are within normal range (0.8-1.1 is generally accepted as normal for OKN).
- Right eye gain of 1.02 and left eye gain of 0.93 are symmetric and appropriate.
- The asymmetry between the two eyes is minimal (~9%), which is not clinically significant (inter-eye asymmetry >25-30% is considered abnormal).
- The waveform traces (red = right, blue = left) show regular, rhythmic saw-tooth nystagmus - this is the expected normal OKN pattern.
- Fast phase angles (~108-121°) are directionally consistent with the downward stimulus direction.
Conclusion for Page 1: NORMAL
Page 2 - Right to Left 10°
| Parameter | Right Eye | Left Eye |
|---|---|---|
| Horizontal Gain | 0.97 | 1.03 |
| Fast Phase Direction | 198.12° | 200.77° |
Interpretation:
- Both gains are well within normal limits and nearly symmetric (right 0.97, left 1.03).
- The inter-eye asymmetry is only ~6%, far below the threshold of concern.
- Fast phase direction (~198-200°) is consistent with a rightward fast phase in response to leftward stimulus movement - this is the expected pattern.
- The waveform traces again show regular saw-tooth patterns consistent with normal OKN.
Conclusion for Page 2: NORMAL
Overall Summary
| Test | Right Eye Gain | Left Eye Gain | Symmetry | Result |
|---|---|---|---|---|
| Top-to-Bottom (Vertical) | 1.02 | 0.93 | Normal | Normal |
| Right-to-Left (Horizontal) | 0.97 | 1.03 | Normal | Normal |
All OKN parameters are within normal limits. There is:
- No significant directional asymmetry (neither eye shows reduced gain relative to the other)
- No evidence of unilateral pursuit pathway lesion
- No directional preponderance suggesting a peripheral or central vestibular abnormality
- Normal gain bilaterally in both horizontal and vertical planes
Clinical significance: Normal OKN testing argues against significant optic tract, posterior parietal cortex, or brainstem pursuit pathway pathology. Combined with normal vertical OKN, there is no suggestion of dorsal midbrain or cerebellar dysfunction either.
Note: As per Cummings Otolaryngology, "slow-phase abnormalities on optokinetic tests parallel those detected with smooth-pursuit testing, whereas quick-phase abnormalities are correlated with those detected on saccade testing." This normal OKN result is most meaningful when interpreted alongside caloric testing, smooth pursuit, and saccade tests in the full vestibular test battery. Clinical correlation with the patient's symptoms is always recommended.
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