What are saccadic abnormalities in multiple sclerosis (MS)?

Updated: Feb 21, 2019
  • Author: Fiona Costello, MD, FRCP; Chief Editor: Hampton Roy, Sr, MD  more...
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Answer

Patients with multiple sclerosis may demonstrate abnormal saccadic intrusions, causing vision loss and oscillopsia. [40, 49] Stable visual fixation is maintained by pause-cell neurons in the brainstem; these are located in the pontine raphe between the two abducens nuclei. [41] Pause cells prevent unwanted saccadic pulses by inhibiting saccadic premotor burst neurons located in the paramedian pontine reticular formation (PPRF) and the midbrain. [41, 49]

One example of a saccadic intrusion that may affect patients with MS is the square wave jerk, which is a quick movement of the eye away from and back to primary position, which occurs with an intersaccadic latency of 150-200 milliseconds. [41, 49] Larger saccadic interruptions with a shorter intersaccadic latency (up to 80 milliseconds) are termed macro square wave jerks. [41] Opsoclonus consists of repetitive bursts of conjugate saccadic oscillations, with horizontal, vertical, and torsional elements. [41] , During each burst of these high-frequency oscillations, the movement is continuous, without an intersaccadic interval. [41]

In ocular flutter, there is no intersaccadic latency, although the pattern is of saccadic eye movement restricted to the horizontal plane. [41] Both opsoclonus and ocular flutter have been described in patients with MS. [49] Variable treatment benefits have been reported with corticosteroids, thiamine, propranolol (40-80 mg orally 3 times daily), nitrazepam (15-30 mg orally daily), and clonazepam (0.5-2 mg orally three times daily). [41]

Patients with MS may also present with features of underactive or overactive saccadic eye function due to altered inputs from the posterior fastigial nuclei and cerebellum (dorsal vermis), which calibrate the size of saccadic pulses. [40] Hypermetric saccades result from damage to the deep nuclei, whereas hypometric saccades arise from damage to the vermis alone. [40] Saccadic dysmetria, particularly of the hypermetric variety, has been reported to affect approximately 40% of patients with MS [49] and frequently contributes to the efferent visual pathway symptoms in this patient population.


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