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To explore the patterns and mechanisms of jerky seesaw nystagmus in internuclear ophthalmoplegia (INO), we analyzed the nystagmus patterns in 33 patients with dissociated torsional-vertical nystagmus and INO. In 11 (33%) patients, the nystagmus was ipsiversive torsional in both eyes with vertical components in the opposite directions. In contrast, 18 (55%) patients showed ipsiversive torsional nystagmus with a larger upbeat component in the contralesional eye. Four (12%) patients exhibited ipsiversive torsional nystagmus with a greater downbeat component in the ipsilesional eye. At least one component of contraversive ocular tilt reaction was associated in most patients (30/33, 91%). The patterns of jerky seesaw nystagmus in INO suggest a disruption of neural pathways from the contralateral vertical semicircular canals with or without concomitant damage to the fibers from the contralateral utricle in or near the medial longitudinal fasciculus. [ABSTRACT FROM AUTHOR]

Abstract: Even though pendular seesaw nystagmus (PSN) or periodic alternating nystagmus (PAN) has been reported in blind persons, the co-occurrence of PSN and PAN has not been described. A 69-year-old woman with progressive visual loss to only light perception in both eyes showed PSN with a conjugate torsional component and the vertical components in the opposite directions in both eyes. In complete darkness, she also exhibited PAN in addition to PSN. PSN remained unchanged in darkness. The rest of the neurological examination, testing for mitochondrial mutations of Leber''s hereditary optic neuropathy, fluorescent angiography, electroretinogram, and brain MRI were normal except for bilateral optic atrophy. Deprivation of the visual inputs, which are required to calibrate normal eye motion, may produce various ocular motor abnormalities in blindness. Although the co-occurrence of PSN and PAN in our patient with visual loss indicates a common etiology, the different effects of darkness on nystagmus intensity suggest a distinct pathomechanism. [Copyright &y& Elsevier]

Abstract: Background: In benign paroxysmal positional vertigo involving the horizontal canal (HC-BPPV), nystagmus may be induced by neck flexion in the pitch plane while sitting (head-bending nystagmus). Objective: To determine the characteristics and lateralizing value of head-bending nystagmus in HC-BPPV. Methods: Using video-oculography, head-bending nystagmus was recorded in 54 patients with HC-BPPV (32 canalolithiasis and 22 cupulolithiasis). Lesion side was determined by comparing intensity of the nystagmus induced by lateral head turning (head-turning nystagmus) in supine. Results: Head-bending nystagmus was observed in 39 patients (72.2%) and lying-down nystagmus in 41 (75.9%). Thirty three patients (61.1%) showed both types of nystagmus while six (11.1%) had only head-bending and another eight (14.8%) showed only lying-down nystagmus. In 45 patients with asymmetrical head-turning nystagmus, the direction of head-bending nystagmus was mostly toward the affected ear in canalolithasis (88.9%) and toward the intact ear in cupulolithasis (80.0%). In 9 (16.7%) patients whose affected ear could not be determined due to symmetrical head-turning nystagmus, the particle repositioning maneuver based on the direction of head-bending or lying-down nystagmus resulted in the resolution of symptom. Two patients showed a transition from canalo- to cupulolithiasis during head-bending posture. Conclusion: In HC-BPPV, neck flexion in the pitch plane while sitting may generate nystagmus by inducing ampullopetal migration of the otolithic debris in the horizontal canal or by ampullofugal deflection of the cupula by the attached otolithic debris. Head-bending nystagmus may be a valuable sign for lateralizing the involved canal in HC-BPPV, especially when patients show symmetrical head-turning nystagmus. Conversion of canalo- into cupulolithiasis by the neck flexion supports the current explanation of the mechanisms of HC-BPPV. [Copyright &y& Elsevier]