Nkispontaneous Nystagmus

Spontaneous Nystagmus • Cause:

– Lesion to peripheral vestibular system

• Imbalance of tonic signals sent to oculomotor neurons from vestibular nuclei • Causes a constant drift of the eyes in one direction

– Vestibular system thinks head is turning away from lesioned side – Eyes are pushed away from the side of the strongest neural input until reach pre-established point where they are interrupted and returned by the fast component in the opposite direction – If due to a peripheral lesion: pursuit system can cancel (except in the ACUTE phase), by having patient open eyes and fixate the nystagmus disappears

Spontaneous Nystagmus – Peripheral vestibular lesions

• Cause diminished tonic afferent signals from all five sensory organs of one labyrinth (3 ampullaris cristae and both maculae)

– Resulting peripheral vestibular spontaneous nystagmus has a combined torsional, horizontal and vertical component » Horizontal is most dominant component due to tonic activity from vertical canals and otolith organs partially canceling each other – Spontaneous nystagmus post acute lesion (eyes open and goes away with fixation) disappears 1-2 weeks post acute peripheral lesion

Spontaneous Nystagmus • Spontaneous nystagmus with eyes closed can be found years later – Can indicate incomplete compensation – Peripheral lesion opposite to direction of nystagmus » Ex. Right beating spontaneous (vision denied) uncompensated left peripheral vestibular lesion – Occasionally irritative lesions can give spontaneous nystagmus toward side of the lesion » Ex. Meniere’s disease

Spontaneous / Positional Nystagmus • Common Classification of unidirectional nystagmus: 

– "1st degree is present only on looking in the direction of the quick phases, – 2nd degree is also present in the central position; – 3rd degree is present on looking in all directions of gaze." 

Page 412 R. John Leigh and David S. Zee "The Neurology of Eye Movements" 3rd edition.

Spontaneous / Positional Nystagmus • Let’s repeat that so it might be more clear…. – "When the nystagmus is direction-fixed (always beating in the same direction), it may be characterized as either 1st, 2nd or 3rd degree. 

• If seen only in one position of lateral gaze then it is called 1st degree; • if seen in lateral gaze and in primary position, then it is called 2nd degree; • and if seen in primary and both lateral gaze positions, it is called 3rd degree." Shepard & Telian 1996

Spontaneous / Positional Nystagmus • Why positional can exist with no spontaneous?

– Past belief was lesions of otolith organs and their connections in the vestibular nuclei and cerebellum caused positional nystagmus • Because these sensory organs are sensitive to changes in direction of gravity

– More recent studies indicate the cupula is altered so that its specific gravity no longer equals that of the surrounding endolymph • This causes the organ to become sensitive to changes in direction of gravity and can produce positional nystagmus

Spontaneous / Positional Nystagmus • Why can positional nystagmus exist with no spontaneous nystagmus? (continued)

– Evidence that both structural and metabolic factors can alter the specific gravity of the cupula and cause positional nystagmus (Honrubia, 2000) – So, positional nystagmus is generally a manifestation of an organic pathology affecting the vestibular system

Spontaneous Nystagmus • What is Significant? – According to Dr. David Cyr (1991)

• Even when mild positional or spontaneous nystagmus occurs in people without Sx (normals) – Note presence, direction and velocity in each position regardless of how minimal the SCV is.

• If patient has a peripheral vestibular lesion the spontaneous and/or positional nystagmus is probably a sign of tonic vestibular imbalance – If both vestibular systems are equal, then nystagmus should not be present

• Remember: patients that see us are not “normal” or would not be in complaining of imbalance/dizziness

Analysis- Spontaneous • Working data tab – Clean up and analyze data • Windowed data tab – Save a selection of data for printing • Loaded data tab – Raw data • When analyzing data you can print the screen – Click print screen button – Additional way to show data of

Analysis- Spontaneous • Filters – Min. Delta

• removes all slow phase components (or any other sloping waveform) with a slope equal to, or less than, the current setting.

Analysis- Spontaneous • Velocity limits filter – remove all data outside max & min velocity limits set on the scale. • Adjust by dragging pointers up/down or • clicking up/down arrows on the level indicators at each end of the scale. • Select Eye – control data viewing/analyzing • ‘Combined’: average response from the left and right eye. • ‘Both’: displays left and right responses together on the same graph. • “Right” or “Left” displays single eye data

Analysis- Spontaneous • Results (Index) – Green cursor indicates laser on/off – Results show the average laser on (fixation) eye velocity (deg/sec) for 1st segment & average laser off (vision denied) eye velocity for 2nd segment – Use the index

Analysis- Spontaneous • Delete Area – Click to display two red cursor lines. – Drag lines to section of data to be removed – Click ‘Done’ – The deleted area will be highlighted in red and then removed from the result calculations. • Delete undesired beats by clicking on them – The deleted velocity beat will be

Analysis - Spontaneous • Windowed Data Tab – Will show the data from Fixation and Vision Denied in each window – If there is data you wish to have in the report or printed • Select the area with the Zoom option you prefer and “Set Window” for both Fixation (laser on) and Vision denied (laser off)

– Will give ASPV for each