Application of binocular vision tests
1. Learning Objectives
By the end of this topic you should be able to:
● Categorise binocular vision (BV) problems using:
○ Cover test
○ Ocular motility
○ History & symptoms
● Use additional BV tests to further understand a BV problem:
○ Mallet unit (fixation disparity / associated phoria)
○ Maddox rod / Maddox wing
○ Suppression tests (Bagolini, Worth 4-dot, etc.)
○ Stereopsis tests (Frisby, TNO, Titmus, etc.)
● Interpret and record BV test results accurately.
● Decide:
○ When no treatment is needed
○ When to manage in practice
○ When to refer (especially for recent incomitant deviations / possible nerve
palsy).
2. Normal vs Abnormal Binocular Vision
Normal Binocular Vision
● Use of both eyes together so that:
○ A single and clear image is perceived.
○ Visual axes are both aligned on the object of regard.
● Any small misalignment is:
○ Within Panum’s fusional area → sensory fusion still possible.
○ Correctable by vergence without symptoms.
● Accommodation:
○ Response is adequate and accurate for the task.
○ No excessive accommodative effort needed to maintain clear, single vision.
Abnormal Binocular Vision
● Single clear vision is not maintained:
○ Visual axes misaligned outside Panum’s fusional area.
, ○ Results in diplopia (double vision), unless suppressed.
● Single clear vision might only be obtained if the patient uses:
○ Excessive / inappropriate accommodative effort
○ Excessive / inappropriate vergence effort
● This leads to asthenopic symptoms:
○ Eye strain, headaches, blur, intermittent diplopia, difficulty with near tasks, gritty
eyes etc.
3. Outcomes of Misalignment of the Visual Axes
When the two visual axes are not directed at the object at the same time you can get:
1. Heterotropia (tropia / squint)
○ Manifest deviation – present even when both eyes are open.
○ One eye is not aligned with the fixation target.
2. Heterophoria (phoria)
○ Latent deviation – only appears when binocular fusion is disrupted (e.g. on
cover test).
○ Under normal conditions, fusional vergence holds eyes straight.
3. Fixation disparity
○ Very small misalignment within Panum’s fusional area.
○ Patient still has single vision but may have symptoms.
○ Measured as associated phoria using a test like the Mallet unit.
4. Cover Test in Adults – Decision Pathway
1. Learning Objectives
By the end of this topic you should be able to:
● Categorise binocular vision (BV) problems using:
○ Cover test
○ Ocular motility
○ History & symptoms
● Use additional BV tests to further understand a BV problem:
○ Mallet unit (fixation disparity / associated phoria)
○ Maddox rod / Maddox wing
○ Suppression tests (Bagolini, Worth 4-dot, etc.)
○ Stereopsis tests (Frisby, TNO, Titmus, etc.)
● Interpret and record BV test results accurately.
● Decide:
○ When no treatment is needed
○ When to manage in practice
○ When to refer (especially for recent incomitant deviations / possible nerve
palsy).
2. Normal vs Abnormal Binocular Vision
Normal Binocular Vision
● Use of both eyes together so that:
○ A single and clear image is perceived.
○ Visual axes are both aligned on the object of regard.
● Any small misalignment is:
○ Within Panum’s fusional area → sensory fusion still possible.
○ Correctable by vergence without symptoms.
● Accommodation:
○ Response is adequate and accurate for the task.
○ No excessive accommodative effort needed to maintain clear, single vision.
Abnormal Binocular Vision
● Single clear vision is not maintained:
○ Visual axes misaligned outside Panum’s fusional area.
, ○ Results in diplopia (double vision), unless suppressed.
● Single clear vision might only be obtained if the patient uses:
○ Excessive / inappropriate accommodative effort
○ Excessive / inappropriate vergence effort
● This leads to asthenopic symptoms:
○ Eye strain, headaches, blur, intermittent diplopia, difficulty with near tasks, gritty
eyes etc.
3. Outcomes of Misalignment of the Visual Axes
When the two visual axes are not directed at the object at the same time you can get:
1. Heterotropia (tropia / squint)
○ Manifest deviation – present even when both eyes are open.
○ One eye is not aligned with the fixation target.
2. Heterophoria (phoria)
○ Latent deviation – only appears when binocular fusion is disrupted (e.g. on
cover test).
○ Under normal conditions, fusional vergence holds eyes straight.
3. Fixation disparity
○ Very small misalignment within Panum’s fusional area.
○ Patient still has single vision but may have symptoms.
○ Measured as associated phoria using a test like the Mallet unit.
4. Cover Test in Adults – Decision Pathway
