Eye Handbook App for OKN

Optokinetic nystagmus (OKN): one way this can be examined virtually is using a smartphone application (e.g. Eye Handbook © app used in this video) or optokinetic tape/flag/drum held in front of the examiner's camera. The optokinetic stimulus should occupy the full screen of the patient's device (easier to elicit and appreciate OKN using a computer screen rather than a smartphone). Instruct the patient to move close to their screen, focus on an area of the screen close to the lens of the camera, and count the stripes as they pass. The slow phases represent smooth pursuit while the fast phases represent saccades. Since the optokinetic stimulus used does not involve full visual field stimulation (e.g., looking out the window at passing scenery from a moving train), this is not a true OKN. Situations in which the virtual or bedside examination [https://collections.lib.utah.edu/details?id=1307320] of OKN can be helpful include: 1) rapid assessment of symmetry and presence/absence of pursuit/saccades in an uncooperative or difficult to examine patient, 2) it can help to bring out a subtle adduction lag in INO [https://collections.lib.utah.edu/details?id=1278693] (3) one of the first ocular motor signs of PSP is loss of the downward fast phase to an optokinetic stimulus directed upward [https://collections.lib.utah.edu/details?id=1290930] (4) if nystagmus is seen in a patient with functional monocular (when the good eye is occluded) or binocular blindness, this suggests that the patient has at least some vision, 5) since upward saccades are often affected in dorsal midbrain (Parinaud's syndrome), vertical OKN can demonstrate this and convergence retraction nystagmus (when stimulus is directed downward).