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I ANATOMY                

 

II PHYSIOLOGY OF        EYE MOVEMENTS 

III EXAMINATION: EYE MOVEMENTS & NYSTAGMUS 

IV FIXATION INSTABILITY   

V SUPRANUCLEAR to NUCLEAR  

 VI VESTIBULAR     SYSTEM 

VIII CN PALSIES, VISUAL FIELDS, PUPIL & THE EYE

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KZVB

Lesions affecting the connections of the inferior olivary nucleus may produce pendular ocular oscillations with vertical or torsional components (about 2 cycles per second). This syndrome is known as oculopalatal tremor and usually develops weeks to months after lesions affecting the nuclei and connections within the Guillain–Mollaret triangle (the inferior olive to deep cerebellar nuclei via inferior cerebellar peduncle, and from deep cerebellar nuclei back to inferior olive via superior cerebellar peduncle, through the red nucleus and central tegmental tract) (Yanagisawa et al., 1999; Shaikh et al., 2010; Tilikete et al., 2011). There may be oscillations of the palate, larynx, and diaphragm. The main pathologic finding is hypertrophic degeneration of the inferior olivary nucleus, which leads to an aberrant synchronous discharge from enlarged neurons in contact with each other through electrotonic conduction mediated by gap junctions (De Zeeuw et al., 1998).

 

Eggers

Although deviating from the original derivation of the word, the term nystagmus has also come to include pathologic oscillations of the eyes in which cycles consist of slow drifts of the eyes that reverse direction periodically, usually at a frequency between 1 and 10 Hz. The appearance of this oscillation resembles the sinusoidal motion of a pendulum and hence is called pendular nystagmus. While some refer to these as “pendular oscillations,” the term pendular nystagmus is too well established in the medical literature to replace it

Frequency: Though measuring beats per second is generally of little value in characterizing vestibular nystagmus, describing the nystagmus frequency (in cycles per second or Hertz) is useful in certain forms of nystagmus such as oculopalatal tremor, oculomasticatory myorhythmia, and the monocular vertical oscillations associated with loss of vision in one eye (Heimann-Bielschowsky phenomenon), which have characteristically low frequencies of 2 Hz or less.

 

6.3. Effect of vergence
Some forms of nystagmus may have a
convergence-divergence component, especially
acquired pendular nystagmus (2.1.3.2.) associated with multiple sclerosis, oculopalatal tremor
(2.1.3.2.1.), and oculomasticatory myorhythmia
(2.1.3.2.2.).

 

Oculopalatal tremor: A form of acquired pendular nystagmus characterized most commonly by large amplitude, low frequency (1–3 Hz), and often disconjugate vertical, torsional and horizontal oscillations [96, 150] that may be enhanced by eye closure [112]. The syndrome of oculopalatal tremor includes synchronous movements of the soft palate and sometimes other muscles derived from the same branchial arch. Comment: The presence of oculopalatal tremor implies dysfunction in the brainstem or cerebellum within the Guillain-Mollaret triangle (the dentato-rubro-olivary tract) and is associated with hypertrophic degeneration of the inferior olivary nucleus. The nystagmus waveform is variable, being less smooth and sinusoidal than the acquired pendular nystagmus typically seen in demyelinating diseases.

 

Oculomasticatory myorhythmia: A form of disjunctive acquired pendular nystagmus characterized by pendular convergence-divergence oscillations at about 1 Hz often associated with synchronous oscillatory movements of the jaw, face, or limbs. Comment: Oculomasticatory myorhythmia is generally accompanied by vertical saccadic palsy and has thus far only been described in central nervous system Whipple’s disease