CONGENITAL NYSTAGMUS WAVEFORMS AND FOVEATION STRATEGY

Accurate eye movement recordings of sixty-five subjects with congenital nystagmus (CN) provides a firm foundation for the classification of the many types of wave­ forms observed and results in objective definitions based on measurable quantities rather than subjective clinical impressions. The careful scrutiny of these records along with the utilization of laser-target retinal cinematography have yielded insights into the mechanism of this ocular motor instability. Prolongation of target foveation emerges as the dominant factor in many of the resultant waveforms. This enhances the visual acuity of the subject with CN. An additional observation, related to fixation bias reversals of the CN subject, may be a physiological indicator of foveal function. Utilization of accurate, DC-coupled eye movement recording techniques in the study of congenital nystagmus (CN) has resulted in the use of com­ posite prisms to improve visual acuity of patients with this disorder (Dell'Osso et aI., 1972; Dell'Osso, 1973; Dell'Osso et aI., 1974). The quanti­ tative recordings and the use of retinal cinematography have provided insights into the genesis of this ocular motor instability and a sounder basis for wavef~rm classification. In this report we will identify previously held beliefs about CN which we have found to be erroneous, and will re-define and classify the nystagmus types and waveforms in a manner based on measurable quantities which are free from confusing and oft-times mis­ leading clinical impressions. Whenever possible, we will relate waveform to the foveation strategy utilized to enhance visual acuity.