Image-shifting optics for a nystagmus treatment device.

Acquired pendular nystagmus (APN) complicates multiple sclerosis and other neurological disorders, causes visual impairment, and is often refractory to available treatments. Vision could be improved by an optical aid that shifts the seen world in lockstep with the APN. An essential component of such a device is the image-shifting mechanism, which must be light, accurate, suitable for battery operation, and capable of image shifting at the frequencies and amplitudes seen in APN. We determined that a three-lens image-shifting mechanism used in commercial image-stabilizing lenses has the potential to satisfy all these requirements. In combination with software designed to track nystagmus, the optical mechanism proved capable of improving visual acuity in 12 normal subjects experiencing simulated two-dimensional nystagmus. Acuity was restored to within an average of 0.12 logMAR (range 0.0-0.22) of the subjects' values without the simulated nystagmus. These results support the feasibility of an assistive device for patients with APN.