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Worth Four-Dot Test

A simple binocular vision test using red-green glasses and four colored lights to assess fusion, suppression, and diplopia.

4 min read

The Worth four-dot test is a quick, simple test of binocular vision and fusion. The patient wears red-green dissociating glasses (red over one eye, green over the other) and looks at a target with four lights - one red, two green, and one white. By reporting how many lights they see and what colors, the patient reveals whether the eyes are working together (fusion), whether one eye is being suppressed, or whether diplopia is present.

Key Takeaways

  • Tests fusion, suppression, and diplopia with a simple red-green dissociation method
  • Performed at distance and at near - sometimes giving different results
  • Useful in strabismus and amblyopia evaluation, including pediatric assessment
  • Quick to perform - usually a couple of minutes
  • Limited by patient cooperation and unequal red-green color perception in some individuals

How the Test Works

The patient wears glasses with a red lens over one eye (typically the right) and a green lens over the other. The four-dot target is arranged in a diamond pattern: one red light at top, one green light on either side (left and right of center), and one white light at the bottom.

  • The red eye sees the red and white lights (the white appears red because of the filter)
  • The green eye sees the green and white lights (the white appears green)
  • Whether and how the patient perceives the four lights together depends on their binocular status

Possible Responses

Response Interpretation
Sees 4 lights If the eyes are straight, normal binocular fusion. In a patient with manifest strabismus, this finding indicates anomalous retinal correspondence (ARC) - the brain has remapped to fuse despite ocular misalignment
Sees 2 red lights Left eye suppression (in the standard red-on-right setup)
Sees 3 green lights Right eye suppression
Sees 5 lights Diplopia - eyes misaligned, no suppression
5 lights with reds and greens uncrossed (reds on right when red lens is on right eye) Esotropia
5 lights with reds and greens crossed (reds on left when red lens is on right eye) Exotropia
Vertical separation of red vs. green lights Vertical (hyper/hypo) deviation

When the eyes fuse, the white light may appear red, green, or alternating/mixed depending on which eye is dominant - this is normal and confirms fusion.

Common Uses

  • Suspected strabismus with concern for diplopia or suppression
  • Amblyopia evaluation - confirming or refuting suppression
  • Post-treatment monitoring of strabismus surgery
  • Prism trials to determine prism prescription
  • Distinguishing functional vs. organic vision loss in some cases

Distance vs. Near

The test is typically performed at distance (6 m or 3 m) and at near (33 cm). The angle subtended by the lights at the retina differs at the two distances, so the test probes different areas of retina:

  • Fusion at near but suppression at distance - can occur in intermittent exotropia, where convergence at near maintains alignment, and in monofixation or microtropia, where the smaller distance target may fall within a central suppression scotoma
  • Fusion at distance but suppression at near - suggests a different or larger suppression pattern and needs clinician interpretation
  • Suppression at both distances - often a large or constant deviation
  • Fusion at both distances - reassuring binocularity on this test

A handheld flashlight Worth four-dot can be brought closer or farther to vary the angle subtended at the retina, which probes peripheral versus central fusion at the bedside.

Limitations

  • Patients must reliably report what they see
  • Color anomalies (red-green deficiency) interfere
  • Cannot be used in very young or pre-verbal children without modifications
  • Provides categorical not quantitative information

Frequently Asked Questions

What does suppression mean?

Suppression is the brain's way of avoiding double vision when the eyes are misaligned. The visual cortex actively ignores input from one eye. It is adaptive in childhood but contributes to amblyopia if persistent.

Is the test painful?

No. The patient simply wears glasses and looks at lights. Most testing takes 1-2 minutes.

Can children take the test?

Yes, with appropriate language about lights and colors. Children too young to reliably report colors need different tests (preferential looking, fixation behavior).

References

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