Certified Ophthalmic Medical Technologist (COMT)

Answer: C - The alternating cover test is used to measure the magnitude and direction of deviation of a phoria or tropia.

The alternate cover test measures total deviation, which includes the tropia plus the phoria. The examiner occludes one eye and then the other during this test, alternating the occluder back and forth between eyes. It is critical to hold the occluder over each eye for at least a few seconds throughout the alternate cover test to provide the non-occluded eye adequate opportunity to pick up fixation.