<unk>  is a tendency of the eyes to drift in the direction of the heterophoria. While the heterophoria refers to a fusion-free vergence state, the<unk>  refers to a small misalignment of the visual axes when both eyes are open in an observer with normal fusion and binocular vision. The misalignment may be vertical, horizontal or both. The misalignment (a few minutes of arc) is much smaller than that of strabismus. While strabismus prevents binocular vision,<unk>  keeps binocular vision, however it may reduce a patient's level of stereopsis. A patient may or may not have<unk>  and a patient may have a different<unk>  at distance than near. Observers with a<unk>  are more likely to report eye strain in demanding visual tasks; therefore, tests of<unk>  belong to the diagnostic tools used by eye care professionals: remediation includes vision therapy, prism eye glasses, or visual ergonomics at the workplace. Fig.1: Visual axes of the two eyes in optimal binocular vision (blue) and in exo and eso<unk>  (black and red, respectively).
Fixation disparity
Auscultatory gap
Place of articulation
Cup-to-disc ratio
Intrinsicoid deflection
Stereoblindness
Joint locking 
Midline shift