Pursuit: • Smooth Pursuit Is Of Minor Clinic Diagnostic Use

Pursuit • Smooth pursuit is of minor clinic diagnostic use: – Results are usually nonspecific – Affected by attention, – Difficulty getting norms and comparing across labs and equipment due to different paradigms – Affected by ability to see and quality of target – Affected by medications – Declines with age – Worse in women

Pursuit • Pursuit gain: – ratio of eye velocity to target velocity • affected by target velocity, acceleration and frequency – In a sinusoidal pursuit stimulus, these three things are interdependent – In a triangular wave pursuit stimulus; » velocity is constant » acceleration appears as periodic pulses » frequency and velocity can be varied independently of acceleration » perfect tracking of the triangular wave stimulus is impossible because of the abrupt accelerations at turnaround time.

Disorders of Smooth Pursuit • Low Gain Pursuit Abnormalities: – Low steady-state pursuit gain (target is maintaining the same speed and patient cannot maintain that eye speed: thus low gain) • Old age • Parkinson’s disease • PSP • Cerebellar disorders • Hepatic encephalopathy (hepato encephalopathy) • Following large cerebral lesions

Disorders of Smooth Pursuit • Low Gain Pursuit Abnormalities:

– Low acceleration pursuit gain (target is accelerating in speed and patient cannot maintain that eye speed: thus low gain) – Posterior cortical lesions – Alzheimer’s disease – Schizophrenia

Disorders of Smooth Pursuit • Pursuit gain greater than 0.8 – good/ normal

• Gain greater than 0.2 < 0.8

– moderate » Rule out inattention, medication, age » Could be CNS disorder

• Gain <0.2 :

– abnormal » CNS disorder

Disorders of Smooth Pursuit • Asymmetric Pursuit (both eyes doing same thing but only one direction of eye movement) – CNS disorder • Acute parietal or frontal lesions – Better pursuit contralateral to lesion – Cortical caused pursuit asymmetry usually only lasts several weeks • Posterior cortical areas and underlying white matter – Easier to pick up with triangular wave paradigm – Abnormality of vertical smooth pursuit • Bilateral INO – Rule out: • unidirectional spontaneous nystagmus overlay • amblyopia (lazy eye)

Asymmetric Pursuit

Disorders of Smooth Pursuit • Disorganized pursuit

– Typical in patients with visual field deficits – Use corrections to find target, but track target fine when can see it

Analysis – Smooth Pursuit

Analysis – Smooth Pursuit • All results relate to the average cycle data. • Average cycle Tab – Shows average cycle and frequency response of acquired data. • Stimulus Results (for researchers) – Fundamental power – amount of energy at fundamental stimulus frequency – Total power – amount of energy over entire stimulus signal – Fundamental phase – phase of the stimulus signal – Stimulus frequency – pursuit tracker sinusoidal frequency, in Hz – Stimulus amplitude – pursuit tracker sinusoidal amplitude, in deg/sec

Analysis – Smooth Pursuit • Response Results: – Fundamental power: • amount of energy at fundamental frequency in patient response – Total power • total amount of energy contained in the patient response signal – Fundamental phase • phase shift between stimulus and patient response signal – Spectral purity • ratio of energy at the fundamental stimulus frequency to total energy (suggested minimum of 50-60%) • A way of judging if the data is good

Analysis – Smooth Pursuit • Response Results (The ones to pay attention to)

– Gain • ratio between slow phase eye velocity and pursuit tracker stimuli – Frequency • calculated frequency of the patient slow phase response – Phase • timing relationship between eye and pursuit tracker movement (in degrees)

Analysis – Smooth Pursuit • Response Results

– Asymmetry (pay attention to) • Ratio in % of maximum slow phase eye velocity of rightward vs. leftward eye movement – Amplitude • maximum average amplitude of the fundamental frequency

Analysis – Smooth Pursuit • Sine filter – Band filter that will flatten any response spikes that pass out of the pre-set boundary when applied.  • The boundaries follow the average response cycles.  • This reduces the velocity response noise, thus improving the spectral purity of the signal. • Filter Position Data – Moving average filter  • This also reduces the velocity response noise, thus improving the spectral purity of