Effects of retinal image stabilization in acquired nystagmus due to neurologic disease

We studied the effects of variable amounts of artificial retinal image stabilization (RIS) upon oscillopsia and visual acuity in eight patients with acquired nystagmus due to neurologic disease. We measured horizontal and vertical eye movements with the magnetic search coil technique and used these electronic signals to control the position of a visual stimulus on a screen in front of the patient. We also used an optical device to stabilize images of the real world upon the retina. During electronic stabilization, RIS was progressively increased until oscillopsia was abolished; this was achieved in all eight patients and corresponded to retinal image drift of 5 degrees/sec or less. In five patients with downbeat nystagmus, further increases in RIS caused the oscillopsia to reappear, but in the opposite direction. Electronic stabilization also improved visual acuity in four of five patients; the limitation of improvement could be related to coexistent visual system defects. Using electronic feedback, we could measure the range of RIS that any individual required to abolish oscillopsia; from this measurement, the components of the optical device that were best suited to provide a stable field of vision could be calculated.