Visual fixation typically suppresses nystagmus caused by a peripheral lesion, but it does not usually suppress nystagmus from a central lesion. It may be therefore be helpful to manipulate a patient's visual fixation to determine whether their nystagmus is due to a central or peripheral lesion.
Frenzel lenses (see attached picture) are large magnifiers that blur vision and inhibit visual fixation. When a patient looks through this type of lens, one would expect peripheral nystagmus to increase, as visual fixation would be inhibited.
If Frenzel lenses are not available, ask the patient to maintain their visual gaze on a single location to reproduce visual fixation. Then note whether the nystagmus ceases (i.e. peripheral lesion) or continues (i.e. central lesion).
