The cover-uncover test can be used to determine the presence or absence of ocular deviation (strabismus).
(1) The patient fixes on a target.
(2) An eye is covered for a few seconds, and then uncovered.
(3) Testing is performed for near and distant fixation.
(4) Testing should be done with and without corrective lenses.
(1) Cover right eye and observe left eye.
(2) If left eye moves, then tropia is present. Uncover right eye and observe both eyes:
(2a) If both eyes move, then there is left monocular tropia.
(2b) If neither eye moves, then alternating tropia.
(3) If left eye does not move, then cover left eye and observe the right eye.
(3a) If right eye moves, then tropia is present. Uncover left eye and observe both eyes:
(3a1) If both eyes move, then there is right monocular tropia.
(3a2) If neither eye moves, then alternating tropia.
(3b) If right eye does not move, then no tropia is present. Alternatively cover right eye, then left eye, and observe uncovered eye:
(3b1) If uncovered eye moves, then phoria is present (see table below).
(3b2) If uncovered eye does not move, then no phoria present (orthrophoric).
• phoria = latent strabismus
• tropias = manifest strabismus
Newly Uncovered Eye
Newly Covered Eye
does not move
does not move, and deviated
nonalternating monocular heterotropia present
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