[Quantitative analysis of the slow phase in congenital nystagmus during convergence]

A previous report described that congenital nystagmus (CN) shows a lower intensity (frequency x amplitude) of spontaneous oscillation during convergence than for distance viewing. However, there has been no detailed report of quantitative analysis of the slow phase of CN during convergence. Therefore, in the present study, the slow phase of CN during convergence was analyzed in 7 patients horizontal and jerky type CN. The time constant of the slow phases were estimated using the repetitive non-linear least square method by a personal computer (NEC, PC 9801). The slow phases of CN for distance viewing were increasing-velocity exponentials, while those of CN during convergence were constant-velocity exponentials. The frequency, amplitude and mean velocity of the slow phase decreased during convergence. Thus, it was suggested that the velocity of the retinal image in CN decreased during convergence.