Optic Flow and Visual Vertigo

Timothy C. Hain, MD, • Most recent update: February 19, 2022

See related pages: Visual dependence.Visual vertigo • Visual-vertigo outline.

A starfield simulation that illustrates optic flow is shown below This program was written by David Inglesias (see Jsfiddle: http://jsfiddle.net/ditman/8Ffrw/). A full screen version is here:

Optic Flow has to do with how things "stream" past. When one is walking through the aisles of a grocery store, there is a "flow field" of visual motion which can be visualized like water going past the prow of a ship. In other words, there is divergence. Objects to the left side are projected as moving leftward on the periphery of the eye, and objects on the right are projected as moving rightward on the periphery of the eye. Ordinarily, the two flow fields cancel out so that there is no net sensation of rotation. When flow processing is asymmetrical or tilted such as in the utricular syndrome, movement through such environments may induce vertigo. Common ocular problems such as difference in the refractive power of one eye vs the other, irregularities in the cornea, interocular lens necessary for cataract removal, and astigmatism can all alter the flow-fields presented to one or both eyes.

Rarely, there are central disorders such as "visual snow" that create flow fields.

For the starfield above, the flow field similar to that used in the Microsoft Windows starfield screen saver. Divergence is zero at the center of the field and maximum towards the extremes.

There are many examples of disturbing Youtube videos that incorporate optic flow: For example:

A few videos from Youtube that illustrate optic flow

 

These videos and many more are sometimes used for training by our vision therapist, Dr. Sorenson, at Chicago Dizziness and Hearing

A few examples of environments that our patients felt disturbing:

Busy environment subsay
Visual environment one patient found to be destabilizing. A New York subway station escalator. -- an expanding visual flow field.

The theory behind visual vertigo:

Persons with impaired vestibular input may weight visual sensation greater than normal persons and become unsteady due to the visual impact. Many times persons with this symptom become faint and have to leave the environment. There is often a panic component.

Patients with vestibular disorders often exhibit increased sway during optic flow. (Redfern et al. 1994).

The flow situation is actually quite a bit more complex than suggested above-- flow fields can be described in terms of four components: translation, expansion, rotation, and shear. Mathematically they can be described using the terms divergence, curl, and deformation of flow with respect to the position of the eye.

These sorts of symptoms can usually be managed by avoidance, conditioning, and dark glasses.

One would expect that anisometropia (difference in optical power between two eyes, often accompanied by spectacles for correction that result in a difference in the size of objects) would cause considerable dizziness, as when the head is moved, there is a potential for the speed of the world movement to vary across eyes. However, the literature is not very supportive of this idea, perhaps because most people can suppress vision in one or the other eye, which they often call "looking out of one eye". Ordinarily people will naturally use the eye with the best vision. One would think that this adaptation would degrade depth perception.

 

References for optic flow

Also see general references regarding visual control of balance