Optic ataxia (Garcin-Rondot) observed in four patients with cerebrovascular disease was evaluated clinically and radiologically (CAT), and its possible mechanism was proposed on the basis of the analysis of our cases and the cases in literature ( Table 1.).     The optic ataxia of Garcin-Rondot is charactereized by the inability to grasp an object presented in the peripheral visual field, while retaining the ability to grasp an object the patient is looking at. This could be explained by the failure of retinal information to reach the PG area of Economo-Koskinas (angular gyrus or Brodmann's 39 area in man), which is shown by an arrow pointing upwards to the left in Fig. 1.. In other words, this means the disturbance of visuo-somatosensory coordination.     On the other hand, in the optic ataxia of Bálint syndrome, grasping of an object is difficult even when the patient is looking at the object, This may be explained by the failure of extraretinal oculomotor information (the upward arrow in Fig. 1 .) to reach the PG area, although in addition retinal information may not reach it.     Possible mechanism of the two types of optic ataxia explained above is summarized in Fig. 6.. The mechanism may be comparable with that of Parinaud syndrome which also has two types, absolute and dissociative.     The mechanism of the optic ataxia of Garcin-Rondot can be mostly explained by the disconnexion theory as mentioned above except for the difference in the symptoms depending on the side of the lesion. In the left cerebral hemisphere lesion, the symptom appears in the right hand in the right homonymous hemivisual field, whereas in the right-sided lesion, it appears in both hands in the left homonymous hemivisual field (Fig^∂.5., lower half).     Thus, there seems to be right cerebral hemisphere dominance in the normal visuo-motor coordination (Fig. 5., upper half), as the right cerebral hemisphere is known to be dominant in space perception and body skill.