To perform the alternate cover test, one eye is covered and then the other, in an alternating fashion, forcing fixation with each eye alternately.
This test is performed after single cover testing as it is the most dissociative of cover tests.
This test will allow the maximal deviation to be determined by alternately covering the eyes and disrupting binocular fusion in order to detect a phoria. By suspending binocular fusion, the test will bring out any phoria which is present in addition to the tropia determined on single cover testing.
The examiner looks at the just uncovered eye as the occlusion is alternated from one eye to the other. This is a method to bring out the maximal deviation present, by breaking fusion: alterate cover testing produces a larger amplitude of phoria than might be seen using the cover-uncover test.
Note that:
- If a tropia is detected by the cover test, the alternate cover test then measures a tropia.
- If no tropia was detected by the cover test, any corrective movement detected by the alternate cover test would be a phoria.
This test involves covering one eye and holding the occluder for several seconds to suspend fusion, then shifting the occluder to the other eye and rapidly alternating back and forth without allowing the patient to become binocular and being careful to always keep one eye occluded. It is important that the patient should never be allowed to regain fusion while the occluder is being transferred.
(vv)TARNSKEW.mp4(tt)
From: Dieterich M, Tarnutzer AA. Bedside ocular motor testing and vestibular testing. EAN 2020.
Using Alternate Cover test to demonstrate a skew deviation
(vv)Alternate Cover Test.mp4(tt)
From: Root T. Ophthalmology Lecture - Tropias & Phorias (part 2/2) Retrieved from: https://www.youtube.com/watch?v=TxEQWtlXtrI
(vv)Alternate Cover Test 2.mp4(tt)
(vv)Ocular_Alignment.mp4(tt)
(vv)Alt Cover Alt Esophoria.mp4(tt)
(vv)Hypertropia Alternate cover test 2.mp4(tt)
(vv)Basic_Eye_Alignment_Exam.mp4(tt)