See-saw nystagmus.

See-saw nystagmus is a rare ocular abnormality, only 15 cases having been recorded to date (Maddox, 1914; Rucker, 1946; Larsen, 1957; Jensen, 1959; Smith and Mark, 1959; Mark, Smith, and Kjellberg, 1960; Lourie, 1963; Schurr, 1963; Kinder and Howard, 1963; Slatt and Nykiel, 1964; and Daroff, 1965). As initially described by Maddox (1914), the eye movements consist of regular reciprocating oscillations in which one eye rises while the other falls. Torsion of the eyes accompanies the vertical movements so that the axis of the rising eye intorts while that of the falling eye extorts. Nine of the reported cases of see-saw nystagmus have been associated with tumours in the region of the optic chiasm and diencephalon. These lesions do not entirely explain the pathogenesis of the seesaw movement, however, since in other cases brainstem or ocular lesions were described instead. Furthermore, in innumerable parasellar lesions seesaw nystagmus does not occur. Much still remains to explain the pathophysiology of see-saw ocular movements. The purpose of the present communication is to present an additional case in which see-saw nystagmus was observed in a patient with bitemporal hemianopia and abnormal vestibular responses. Attention is directed to several of the previously reported cases in which abnormal vestibular responses were also noted. A mechanism is suggested by which see-saw nystagmus is produced by various combinations of visual, vestibular, or other lesions rather than by a lesion in a single anatomical site.