[Quantitative evaluation of nystagmus by an image-analysis system]

We attempted to apply a newly developed image-analysis system for measurement and analysis of nystagmus.

Eye movements were recorded by digital video through a head-mounted charge coupled device (CCD) camera. The recorded movie was converted into black and white in order to detect the area of the pupil. Horizontal and vertical eye positions were determined by calculating the centroid of the pupil. Torsional angle was calculated using the iris striate pattern around the pupillary margin.

The parameters (amplitude, cycle, etc.) of nystagmus were calculated easily by the new image-analysis system from the recorded images. As examples, the foveation period was measured accurately in a case of jerky-type congenital nystagmus. Very regular cycles of intorsional attack period were revealed in a case of superior oblique myokymia. A case of cork-screw-like nystagmus showed a characteristic combination of large and small cycles unassociated with torsion.

This image-analysis system was useful for quantitative analysis of nystagmus, and especially for measurement of torsion. Detailed waveforms and specific rhythms of nystagmus, which could not be recognized by observation, were demonstrated by this system.