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Richard V. Abadi, Columba J. Scallan; Waveform Characteristics of Manifest Latent Nystagmus. Invest. Ophthalmol. Vis. Sci. 2000;41(12):3805-3817.
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© ARVO (1962-2015); The Authors (2016-present)
purpose. To examine the waveform characteristics of 37 subjects with manifest
latent nystagmus (MLN) and determine the manner in which visual
feedback influences the nature of the waveform.
methods. Binocular recordings of the eye movements of all subjects were
undertaken using an infrared tracking system. Subjects viewed
the target binocularly and monocularly in primary gaze. The effect of
visual feedback on the nature of the MLN waveform was examined by
either removing the fixation target or by progressively stabilizing the
target in relation to the retina. This progressive stabilization was
achieved by feeding back the eye movement signal to move an otherwise
results. Four types of MLN were distinguished on the basis of the fixation
characteristics seen during binocular and monocular viewing. First,
under binocular viewing conditions, subjects could theoretically
exhibit stable fixation (type 1 MLN). In addition, three other MLN
types were recorded during binocular fixation: conjugate horizontal
square-wave jerks (type 2 MLN), conjugate torsional nystagmus (type 3
MLN) and conjugate horizontal jerk MLN waveforms (type 4 MLN).
Monocular viewing always gave rise to a conjugate horizontal jerk MLN
waveform for each of the four types of MLN. More than 80% of the
subjects exhibited either type 3 or type 4 MLN, both of which conform
with previous classic descriptions of MLN. Much less common was type 2
MLN. Type 1 MLN (conventionally referred to as a latent nystagmus)
appeared to be a rare occurrence. In addition to the two classic linear
and decelerating MLN slow phases, four additional slow-phase shapes
with either saccadic or pendular elements were recorded and described.
Removing visual feedback generally reduced the mean slow-phase velocity
and the number of fast phases. For each subject some variability of the
slow-phase class was documented from session to session.
conclusions. Four types of MLN have been described. Their differences are based on
their binocular oculomotor behavior, and it is proposed that type 1 MLN
and type 4 MLN represent the absolute states and types 2 and 3 the
intermediate levels of the MLN spectrum. All types of MLN appear to be
strongly visually driven and are largely dependent on the attentional
state of the subject and the target conditions. Six different classes
of slow phase were found among the four MLN types. The introduction of
visual feedback had an immediate effect on the subsequent slow phase or
fast phase. It is likely that adaptation mechanisms are in play after a
period of visual feedback.
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