Prism cover test

Prism Cover Test

The prism cover test is a clinical procedure used in ophthalmology and optometry to assess the presence and magnitude of strabismus, which is a misalignment of the eyes. This test is particularly useful for measuring the angle of deviation in patients with heterotropia or heterophoria.

Prism cover test demonstration

Procedure

The prism cover test involves the use of prisms, which are optical devices that bend light. The test is typically performed in two main steps: the cover-uncover test and the alternate cover test.

Cover-Uncover Test

In the cover-uncover test, the patient is asked to fixate on a distant or near target. One eye is covered with an occluder while the other eye is observed for any movement. If the uncovered eye moves to take up fixation, it indicates a manifest deviation, or tropia.

Alternate Cover Test

The alternate cover test is used to measure the total deviation, including both the manifest and latent components. The occluder is alternated between the two eyes, breaking binocular fusion. Prisms of increasing power are placed in front of one eye until the movement of the eyes is neutralized, indicating the angle of deviation.

Types of Deviations

The prism cover test can help identify different types of deviations:

• Esotropia: Inward turning of the eye.
• Exotropia: Outward turning of the eye.
• Hypertropia: Upward turning of the eye.
• Hypotropia: Downward turning of the eye.

Clinical Significance

The prism cover test is an essential tool in diagnosing and managing strabismus. It provides quantitative data on the angle of deviation, which is crucial for planning treatment strategies such as prism glasses, vision therapy, or strabismus surgery.

Related Pages

• Strabismus
• Ophthalmology
• Optometry
• Prism (optics)
• Vision therapy