Absence of Visual Sampling in Infantile Nystagmus

The possibility that patients with infantile nystagmus achieve spatial constancy by sampling the visual scene only during certain range of velocities or certain phases of their nystagmus cycle was investigated by asking patients to detect a flashed test target that was presented repeatedly during all phases of the nystagmus cycle. After observing a 543 nm fixation spot projected on a diffusely illuminated tangent screen 1m in front of the eye,ﾷ patients were asked to detect a 2 msec test flash of the spot, now locked to the retina, that occurred 200 msec after the fixation spot was extinguished. The test target appeared randomly at 3,6,9, or 12 o´clck at, in separate trials, 0.8 deg or 10.0 deg from central vision. To avoid forcing patients from guessing a direction cued by the diappearance of theﾷ fixation spot, sometimes the flash did not occur at all. To avoid dark adaptation in our patients, the diffuse background illumination was adjusted to the brightest level allowing easy detection of the test flash.