[The physiopathology of supranuclear structures in oculomotor disorders]

Several structures, located at different levels in the Central Nervous System (CNS), collaborate to the control and realization of ocular movements (O.M.) Therefore, alterations of oculomotricity, of varying degree and of different kinds, may be found in a lot of diseases of the CNS. The study of O.M., expecially when carried out by means of specific techniques such as electro-oculography, may represent an useful tool in the diagnosis (both from a topographic and an etiological standpoint) and in the follow-up of patients, possibly also allowing a precise evaluation of therapy effectiveness. In this review the Authors briefly examine the role of the supranuclear structures mostly involved in the control and in the execution of oculomotricity and the characteristics of the different types of O.M. (rapid and slow, vergence movements). Successively, they analyze the semeiological features of supra-nuclear disturbances of O.M., describing alterations of saccadic movements (slowing, dysmetria) and of smooth pursuit, fixation instability (square waves, flutter, opsoclonus, nystagmus,...) and other alterations of O.M. (ocular bobbing, see-saw nystagmus, skew deviation,...). Successively, disturbances of O.M. are analyzed in relation to their topodiagnostic significance, describing oculomotor involvements due to focal lesions of different areas of CNS (frontal cortex, parieto-occipital cortex, basal ganglia, cerebellum, brainstem) and particular syndromes (Foville syndromes, locked-in syndrome, Parinaud syndrome, anterior internuclear ophthalmoplegia, "one and a half" syndrome, Balint syndrome,...). Finally, particular attention is drawn to the oculomotor disturbances observed in degenerative cerebellar and multisystemic diseases, and several abnormal "oculomotor patterns", which seem to be specifically related to particular diseases, are described. In particular, the oculomotor patterns of Steele-Richardson-Olszewsky disease (slowing and hypometria of horizontal saccades, loss of upward saccades with preservation of reflex movements) and of Friedreich ataxia (fixation instability mostly due to the occurrence of square waves, saccadic dysmetria, impairment of smooth pursuit) are stressed.