The instrument can be swung through 90 to measure any vertical fixation disparity.

There are several methods to quantify fixation disparity.

Fixation disparity exists when there is a small misalignment of the eyes when viewing with binocular vision.

A patient's associated phoria is the amount of prism needed to reduce their fixation disparity to zero minutes of arc.

Current research in visual neuroscience and psychophysics is investigating how microsaccades relate to fixation correction, control of binocular fixation disparity and attentional shifts.

A patient may or may not have fixation disparity and a patient may have a different fixation disparity at distance than near.