Oscillopsia, retinal image stabilization and congenital nystagmus

Most individuals with congenital nystagmus (CN) do not complain of oscillopsia (visual inconstancy) even though the amount of retinal image slip varies considerably according to gaze angle and CN waveform. We induced oscillopsia in four subjects with CN by artificially stabilizing images upon the retina under several conditions. Every subject reported oscillopsia during retinal image stabilization, but the condition of stabilization varied from one individual to another. Our results indicate that a variety of mechanisms operate to maintain spatial constancy in congenital nystagmus; some individuals appear to use one mechanism more than another. Possible mechanisms include use of extra-retinal signals, elevated threshold for motion detection and "suppression" of visual input except during foveation periods.