Saccadic Intrusions and Dysmetria

Saccadic dysmetria, intrusions, and oscillations are often encountered in association with certain cerebellar and neurodegenerative diseases. When severe, they can give rise to visual symptoms, such as difficulty with reading and oscillopsia. In this chapter, we begin by reviewing the clinical features of saccadic dysmetria, in which the saccadic amplitude is inappropriately calibrated. We next review the clinical features of saccadic intrusions and oscillations, which include square-wave jerks, macrosaccadic oscillations, ocular flutter, and opsoclonus. We review the common causes of these entities and discuss the diagnostic workup. Lastly, we discuss potential medical treatments to reduce the magnitude and frequency of saccadic intrusions and oscillations.

Otoneurological findings prevalent in hereditary ataxias

ABSTRACT Objective To describe and compare the vestibular findings most evident among the hereditary ataxias, as well as correlate their clinical features with the nervous structures affected in this disease. Methods Seventy-five patients were evaluated and underwent a case history, otorhinolaryngological and vestibular assessments. Results Clinically, the patients commonly had symptoms of gait disturbances (67.1%), dizziness (47.3%), dysarthria (46%) and dysphagia (36.8%). In vestibular testing, alterations were predominantly evident in caloric testing (79%), testing for saccadic dysmetria (51%) and rotational chair testing (47%). The presence of alterations occurred in 87% of these patients. A majority of the alterations were from central vestibular dysfunction (69.3%). Conclusion This underscores the importance of the contribution of topodiagnostic labyrinthine evaluations for neurodegenerative diseases as, in most cases, the initial symptoms are otoneurological; and these evaluations should also be included in the selection of procedures to be performed in clinical and therapeutic monitoring.

The Cerebellum and its Syndromes

discusses a wide range of cerebellar syndromes and links them to specific topographic areas of the cerebellum. The hereditary ataxic syndromes include spinocerebellar ataxia, the Louis-Bar syndrome, spastic ataxia of Charlevoix-Saguenay, and the syndrome of the dorsal vermis. Oculomotor syndromes of the cerebellum—the syndrome of the flocculus/paraflocculus (tonsil), characterized by downbeat nystagmus; the syndrome of the nodulus and uvula, resulting in periodic alternating nystagmus; the syndrome of the fastigial nucleus, responsible for saccadic dysmetria; and the pancerebellar syndrome, characterized by paraneoplastic opsoclonus or flutter—are illustrated by six case studies in this chapter.

Normal Spatial Attention But Impaired Saccades and Visual Motion Perception After Lesions of the Monkey Cerebellum

Lesions of the cerebellum produce deficits in movement and motor learning. Saccadic dysmetria, for example, is caused by lesions of the posterior cerebellar vermis. Monkeys and patients with such lesions are unable to modify the amplitude of saccades. Some have suggested that the effects on eye movements might reflect a more global cognitive deficit caused by the cerebellar lesion. We tested that idea by studying the effects of vermis lesions on attention as well as saccadic eye movements, visual motion perception, and luminance change detection. Lesions in posterior vermis of four monkeys caused the known deficits in saccadic control. Attention tested by examination of acuity threshold changes induced by prior cueing of the location of the targets remained normal after vermis lesions. Luminance change detection was also unaffected by the lesions. In one case, after a lesion restricted to lobulus VIII, the animal had impaired visual motion perception.