Foveation period and waveforms of congenital ocular nystagmus.

Normal visual acuity requires a stationary retinal image on the fovea. If fixation instabilities cause movement of the retinal image across the fovea for a few degrees, visual acuity is diminished. Nystagmus as the fixation instability, consequently, may impair vision. Period of foveation is the area in the wave form, i.e. a brief period of time when the eye is still and is pointed at the object of regard. At this period eye velocity is at a minimum and visual acuity is the best. In the children with congenital ocular nystagmus, using usual clinical equipment (TC 1.0 and TC 0.3 s), was performed electronystagmography (ENG) and analysis of the obtained nystagmus waveforms. In the some patients visual acuity was also examined. The ENG records were classified according to Dell'Osso criteria for waveforms. The findings of jerk nystagmus with extended foveation (J(EF)) and of bidirectional jerk nystagmus (BDJ) were singled out. Foveation time, measured in these weveforms was compared with the visual acuity. Visual acuity was better in the jerk nystafmus weveforms with extended foveation period (J(EF)) than in bidirectional jerk nystagmus with shorter foveation time.