The unilateral (cover-uncover) cover test is an objective method used to determine the presence of a strabismus and differentiate it from a heterophoria. One eye is covered with an opaque occluder while the patient fixates on a target. The uncovered eye is observed for movement during the cover phase, indicating a manifest deviation. If movement is not observed from either eye, move on to the alternate cover test to quantify any heterophoria.

A condition where only the non-strabismic eye can maintain fixation while both eyes are open. The deviated eye is typically suppressed to avoid diplopia. In young children, constant unilateral strabismus is amblyopiagenic if left untreated.