The Cover Test
Phoria vs Tropia


  1. Have the patient view a distant target (the test is also performed at near).

  2. While you observe the right eye, use the occluder to cover the left eye.  One of two things will happen:

    1. If the right eye does not move and remains fixed on the visual target, then the right eye is not tropic.

    2. If the right eye is observed to move in order to take up fixation,  then the eye is tropic and the tropia is identified according to the direction the eye moved from,  and which eye it is that moved. A shift is evidence that the uncovered eye was not regarding the target with its fovea while both eyes were viewing

  3. Remove the occluder from the left eye and allow the patient's gaze to stabilize on the target.

  4. Now cover the right eye with the occluder while you observe what happens to the left eye.  As discussed above,  the left eye will either remain straight, or it will move from a deviated position to take up fixation.

In practice the cover and uncover tests are performed together. ie. cover left eye, watch right eye for tropia. Uncover left eye, watch left eye for phoria. Rpt in other eye.