Spectral analysis of pendular waveforms in congenital nystagmus.

We analyzed quantitatively electronystagmographic recordings of pendular waveforms via spectral analysis methods. We found (1) symmetrical pendular oscillations in orbital positions spanning a range as wide as 40 degrees, with frequencies between 2 and 8 Hz; (2) stable and small pendular oscillations in patients without a null zone and unstable and large pendular oscillations in patients with a neutral zone; (3) a non-decreasing relationship between the amplitude and the frequency of the eye oscillations, and (4) pendular components in orbital positions at the two sides of a neutral zone. It is argued that pendular nystagmus can be generated independently of normal (jerk) nystagmus in the same orbital position.