When all subjects were grouped together, we found no evidence of a consistent horizontal or vertical OKN asymmetry in healthy adults for either look or stare OKN with any combination of velocity, contrast, luminance modulation of grating, or field shape. Although an absence of horizontal OKN asymmetry was expected, the absence of vertical asymmetry was surprising because most of the published literature suggests an upward asymmetry in adults with normal vision (Proudlock FA, et al.
IOVS 2001;42:ARVO Abstract 300).
5 7 9 10 11 12 13 14 15 16 With the use of EOG, Tashahaki et al.
7 found an upward asymmetry in adults with target stimuli of 70°/s and greater, whereas LeLiever et al.
10 found an upward preference for target velocities below 70°/s. More sensitive magnetic search coil techniques used by van den Berg et al.
5 found an upward asymmetry with target velocities ranging from 9°/s to 57°/s. Ogino et al.
9 found an upward asymmetry for target velocities ranging from 30°/s to 90°/s, with a maximum response at velocities of 30°/s to 40°/s. Wei et al.
13 14 also found a consistent vertical asymmetry at 40°/s. In recent studies using videooculography, Garbutt et al.
11 found an upward preference for stimuli velocities of 10°/s to 50°/s, and Proudlock et al. (
IOVS 2001;42:ARVO Abstract 300) found the same for velocities of 10°/s, 20°/s, and 40°/s. The relative contribution of the peripheral and central retina on vertical OKN has been investigated by Murasugi et al.,
16 who found an upward preference with target velocities ranging from 10°/s to70°/s for large field targets (61° × 64°). This asymmetry tended to be exaggerated by biasing stimulation of the peripheral retina and diminished by biasing stimulation of the central retina. Clémant et al.
12 are the only investigators of look OKN vertical asymmetry, and they found an upward preference at 39°/s and 51°/s.