Vertical and oblique saccadic eye movements.

The peak velocities of saccadic eye movements (saccades) in vertical and horizontal directions were determined in 43 normal subjects using a television system which permits accurate tracing of the corneal image of a small light source. The average peak velocity of a 20 degree horizontal saccade was 420 degrees sec-1 which is in the range of previous reports. The peak velocities of 20 degree saccades were compared between right and left eyes, men and women, and among three age groups and four directions. The rightward saccade was faster than the leftward saccade. Age and sex differences were also found; the peak velocities were less in aged than in adult and they were lower in women than in men. Downward saccade was slower than abduction, adduction and upward saccades. In four normal subjects, oblique saccades were recorded with the same system. The saccades were divided into horizontal and vertical components. The relationship between the peak velocity of the horizontal components and the direction of saccades was studied. The horizontal components had the maximum velocity when the saccade was in the horizontal direction, and the velocity decreased as the obliquity of the direction increased. However, such a peak of the velocity-direction relationship was not pronounced in the vertical components of the saccades, although the velocity of the vertical component showed the maximum in the vertical direction of the saccades. Transient adduction movement was found to be associated with vertical and oblique saccades. This adduction caused the trajectories of the saccades to deviate from linearity. The size of the adduction averaged 1.8 degrees for the 20 degree vertical saccade. Thus the vertical saccade system appears to have an involuntary association with the horizontal eye movement system.