To determine visual sensitivity in patients with latent nystagmus with or without esotropia or exotropia, and in patients with esotropia or exotropia, pupillary reactions to 5 degrees diameter light stimuli given to the retina at the fovea (centre), at 5 degrees nasal to the centre, and at 5 degrees temporal to the centre, were measured using electronic infrared pupillography; then pupillary constriction rates and maximum velocity of pupillary constrictions were calculated and analysed. In non-dominant eyes, visual sensitivities of the nasal retina and temporal retina were higher compared with normal eyes, and they also tended to be higher than the sensitivities at the fovea (centre), particularly in patients with latent nystagmus with esotropia. In patients with esotropia or exotropia, visual sensitivities in non-dominant eyes of the nasal retina, and temporal retina increased to a level similar to those at the fovea (centre). The magnitude of these abnormalities was greater in patients with latent nystagmus with esotropia, those with latent nystagmus, and those with latent nystagmus with exotropia, esotropia, and exotropia, in that order. From these results, it was assumed that this imbalance is transmitted to the motor system, resulting in the onset of latent nystagmus.