Cover test

Cover test is a clinical examination used to determine the presence of strabismus, a condition where the eyes do not properly align with each other when looking at an object. The test is performed by covering each eye sequentially while the patient focuses on a distant object.

Procedure

The cover test is performed by having the patient focus on a small object at a distance. The examiner then covers one eye with an occluder. If the uncovered eye moves to pick up the fixation target, it indicates that the covered eye was the one initially fixing on the object. This is known as a positive cover test result and indicates a strabismus.

Types of Cover Tests

There are three types of cover tests: the unilateral cover test, the alternating cover test, and the prism cover test.

Unilateral Cover Test

The unilateral cover test, also known as the cover-uncover test, is used to determine whether the patient has a phoria (latent strabismus) or a tropia (manifest strabismus).

Alternating Cover Test

The alternating cover test, also known as the cross cover test, is used to determine whether the patient has a phoria or a tropia. It is also used to measure the magnitude of the deviation.

Prism Cover Test

The prism cover test is used to measure the amount of deviation in strabismus. It is the most accurate test for measuring the angle of deviation.

Interpretation

A positive cover test indicates that the patient has strabismus. The type of strabismus can be determined by the type of movement seen in the uncovered eye. If the eye moves inwards, it indicates exotropia (outward turning of the eye). If the eye moves outwards, it indicates esotropia (inward turning of the eye).

See Also

• Strabismus
• Exotropia
• Esotropia
• Phoria
• Tropia

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