Bitesize Orthoptics - Cover test simplified
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The Cover Test is a fundamental part of any orthoptic assessment. It helps detect and measure strabismus (eye misalignment) and provides valuable insights into a patient's binocular vision and control. This guide walks you through the two main types: the Cover-Uncover Test and the Alternate Cover Test, including what to observe and how to interpret the results.
The Cover Test is a vital part of your Orthoptic assessment. It helps you detect and measure strabismus, and provides information into a patient’s binocular vision and control. Today’s Bitesize Orthoptics post will walk you through the 2 main types of cover test: 1. The Cover-Uncover Test and 2. The Alternate Cover Test.
The Cover-Uncover Test
This test is designed to detect manifest deviations (tropias).
How to Perform:
Test at near (1/3m) and distance (6m).
Perform the test with and without glasses if applicable.
Use an opaque occluder to cover one eye.
Carefully observe the movement of the uncovered eye while the other is being occluded.
What to Look For:
If a manifest deviation is present, the uncovered eye will move to take up fixation. The direction of this movement helps determine the type of deviation:
Temporal (outwards movement) → Esotropia
Nasal (inwards movement) → Exotropia
Downwards movement → Hypertropia
Upwards movement → Hypotropia
No movement → No manifest deviation
Information Gained from the Cover-Uncover Test:
Type of deviation: Esotropia, Exotropia, Hypertropia, Hypotropia
Size of deviation: Slight, Moderate, Marked
Speed of fixation: Rapid or slow (can indicate visual acuity)
Rapid fixation suggests good vision.
Slow fixation or wandering eye may indicate poor vision or non-central fixation.
Fixation preference:
Alternating fixation may suggest equal vision in both eyes.
Unilateral deviation points to a dominant eye and possibly reduced vision in the other.
The Alternate Cover Test
This test is used to detect latent deviations (phorias) and measure total deviation.
How to Perform:
Test at both near (1/3m) and distance (6m).
Use the occluder to alternate between both eyes, ensuring complete dissociation. At no point should both eyes be uncovered as this will not show you the complete dissociation.
Watch the uncovered eye closely for movement as the cover is switched.
Repeat the Cover-Uncover Test after to ensure full recovery (to check if the deviation remains latent or has become manifest).
Information Gained:
Type of deviation: Exophoria, Esophoria, Hyperphoria, Hypophoria
Size of deviation: Slight, Moderate, Marked
Rate of recovery: Indicates strength of motor fusion and control
Rapid recovery: Good control
Moderate/Slow/Delayed recovery: Weaker control or reduced fusion ability
Decompensation: if the deviation breaks down from latent to manifest
Summary
Together, The Cover-Uncover and The Alternate Cover tests are essential in determining:
Whether a deviation is manifest or latent
The type, size, and control of the deviation
The quality of vision and fixation behavior
Understanding these subtle eye movements is key in diagnosing and managing strabismus effectively. With regular practice, these tests will become second nature and form a solid foundation in your orthoptic skillset.
