The cover–uncover test is used to differentiate if a misalignment is either a tropia or a phoria; that is, if the above cover test demonstrates no tropia, it is used to determine if a phoria (i.e. latent strabismus) is present. Large ones can be associated with asthenopia (i.e. eye strain) and diplopia.

Why is cover test done?

 Cover testing can be done to measure a deviation at near, which requires an accommodative target held at a distance of 33cm for fixation.  It can also be done to measure a deviation with distance fixation.

How do you check your eye alignment at home?

Hold a torch 1 metre in front of the eyes and look for the light reflex on the cornea (Hirschberg test). In the primary gaze (looking straight ahead at the torch light), the light reflexes should be in a symmetrical position on each cornea (Figure 1).