Cover-Uncover Test
Cover testing is the gold standard for the objective method of determining the presence, type, and magnitude of ocular strabismus
Cover testing can be done at both near and distance
When performed at near, an accommodative fixation target is held at a distance of 33 cm
At distance, the patient fixates on a target at a distance of 6 m
Cover-Uncover Test
The cover-uncover test is generally performed first
This test is useful to identify a tropia and differentiate it from a phoria
The test is performed by using an opaque or translucent occluder to cover one eye
The occluder is held in front of the eye for a few seconds and then removed
When the fixing eye is occluded, the examiner will observe the nonoccluded eye move to pick up fixation if a tropia is present
If no tropia is present, the nonoccluded eye will remain stationary
To assess for a phoria, or latent deviation, the examiner observes the eye behind the occluder
If a phoria is present, the uncovered eye does not move; however, the eye that is behind the occluder will deviate and return to a straight position when the occluder is removed
In this patient we can see a left exotropia
When the right eye is covered, we can see the left eye is moving inwards to take up fixation
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Video from Rajan Eye Care Hospital
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