Cover Test

Types of Cover Tests

1. Cover-Uncover Test

Purpose:

Detects manifest deviations (tropias)

Procedure:

- Patient fixates on target

- Examiner covers one eye completely for 2-3 seconds

- Observe uncovered eye for movement

- Repeat on other eye

Interpretation:

- Movement of uncovered eye indicates tropia

- No movement indicates no manifest deviation

2. Alternate Cover Test

ReasearchGate

Purpose:

Reveals total deviation (both manifest and latent)

Procedure:

- Patient fixates on target

- Alternately cover each eye without allowing binocular vision

- Continue for several cycles

- Observe movement when switching cover

Interpretation:

- Movement indicates phoria or tropia

- Larger movements than cover-uncover suggest additional latent component

Direction of Movement and Corresponding Deviations

- Inward movement: Exodeviation

- Outward movement: Esodeviation

- Downward movement: Hyperdeviation

- Upward movement: Hypodeviation

Testing Distances

1. Distance (6 meters/20 feet):

- Tests distance vision

- Uses distant target (usually letter chart)

2. Near (33-40 cm):

- Tests near vision

- Uses accommodative target (usually detailed picture or text)

Clinical Pearls

1. Essential Testing Conditions:

- Good illumination

- Appropriate fixation targets

- Patient wearing habitual correction

- Alert and cooperative patient

2. Common Pitfalls to Avoid:

- Translucent occluder

- Incomplete occlusion

- Too brief occlusion time

- Poor patient attention

3. Documentation Requirements:

- Direction of movement

- Magnitude of deviation

- Testing distance

- Type of deviation (phoria/tropia)

Clinical Significance

1. Diagnostic Value:

- Differentiates between phoria and tropia

- Identifies intermittent strabismus

- Quantifies deviation magnitude

- Determines the direction of deviation

2. Treatment Planning:

- Guides surgical planning

- Helps monitor progress

- Assists in prism prescription

Limitations

- Requires patient cooperation

- May be difficult in young children

- Accuracy depends on the examiner expertise

- Not suitable for patients with poor vision or fixation

When to Perform

1. Routine Screening:

- New patient evaluations

- Pediatric eye examinations

- School screenings

2. Specific Indications:

- Complaints of diplopia

- Suspected strabismus

- Post-strabismus surgery

- Regular monitoring of known deviations

Conclusion

The cover test remains the gold standard for detecting and measuring ocular deviations. Its simplicity, reliability, and non-invasive nature make it an indispensable tool in orthoptic practice.

Note : This document serves educational purposes exclusively and does not constitute medical advice or treatment guidelines