Nkioptokinetics (opk Or Okn)

Optokinetics (OPK or OKN) • Testing requires a full visual field stimulus – At least 90% of vision field

– If using a light bar you are testing smooth pursuit and OPK/OKN but not OKN alone • May get normal results when not normal – If the patient can see any visual marks in the room they may not be able to be tested accurately • The optokinetic system is evaluated by both nystagmus during visual stimulation (OPK/OKN testing) and after (OKAN- the optokinetic afternystamus) – This indicates a normal functioning central vestibular/ velocity storage mechanism

Optokinetics (OPK or OKN) • Need full field to also trigger the sense of rotation known as circular vection

– OPK is centrally mediated • Basford et al. 2003 found 4 of 10 TBI patients did not generate OPK and none had circular vection

Optokinetics (OPK or OKN) • Instructions to the patient influence the results! – If instructed to follow the dots you get prolonged slow phases with large corrective saccades • Look nystagmus – If instructed to stare straight ahead you get small quick phases that are frequent • Stare nystagmus – Best Instructions are none • If patient is falling asleep… – Have them look for the “ red heart”, or “ the star shape”, etc.

Abnormalities: Optokinetics • Low Gain

– Both directions – CNS Lesion • Examples: floccular lesion, parietal lobe lesion – Rule out • large or multiple visual field deficits • Inattention • medications

Abnormalities: Optokinetics • Asymmetric OPK/OKN

– Vestibular end organ • If reduction opposite of spontaneous nystagmus • If acute • IF there is no spontaneous nystamus and not acute – Then it is supra-tentorial – Likely parietal lobe lesion

– Rule out • Visual field deficit (one hemifield)

Supratentorial www.Musckids.com www.wikipedia.com

Analysis – OKN (OPK)

Analysis – OKN (OPK) • % to remove segment ends

– Removes a % from each end of a test segment. • Increasing the % causes more data to be deleted from each end and less to be used for calculation. • The result is based solely on the data remaining between the green cursors.

• Stimulus Noise Filter:

– Same function as sine filter (remove high frequency component of the signal), but to the OKN feedback signal. • Make sure it is always on.

Analysis – OKN (OPK) • Segment: – Moves the green cursors along the data – Selects each segment in turn – The results are shown for the current segment selected

Analysis – OKN (OPK) • Avg Eye Vel – average SPV • StDev – standard deviation for average SPV • Validity – The percentage of the total SPV data that matches the best fit line. – As this number approaches 100%, the results will become more valid. • Avg Stimulus vel – – Velocity of the

OKN, norms