Worth 4 Dot Test: Setup, Responses and Interpretation

Updated 2026-10-22

Written by the Optics Trainer team from published research, with every source linked below.

The Worth 4 Dot test is a quick way to check for fusion, suppression or diplopia. It has been used since Worth described it in 1903 and needs only a light and a pair of red/green glasses. Its simplicity hides some real limits: the filters dissociate strongly, target size changes with distance, and the result is qualitative. This guide covers setup, how to read responses, what near and distance results imply, and what studies show about its reliability and agreement with other tests.

How the test works

The patient wears red/green glasses and views four lights: typically one red, two green and one white. Because each filter blocks the other colour, each eye sees only part of the target, and the combined percept shows whether the eyes fuse, one eye is suppressed, or the patient sees double.

Because the white light is seen through both filters, the counts follow from the filter arrangement. With the red filter over the right eye, the usual reading is: four lights means fusion; two red lights only means the left eye is suppressed; three green lights only means the right eye is suppressed; and five lights means diplopia. Always confirm which filter is over which eye, because the expected counts depend on it.

Near versus distance: what target size tells you

The flashlight version is conventionally done at 33 cm and at 6 m. Near testing is taken to reflect peripheral fusion and distance testing more central fusion, because the angle the lights subtend shrinks as the test distance increases. Webber and colleagues note that the dot separations commonly used subtend about 6 degrees in the 33 cm near test and about 1.25 degrees in the 3 m distance test. So suppression at distance but not at near implies a smaller, more central suppression zone. In 26 previously treated adults with amblyopia, smaller, more central targets revealed more suppression on both the Worth 4 Dot test and a synoptophore (Plaumann and colleagues, 2023).

Moving the flashlight to vary target size may also change accommodative and vergence demand, which complicates interpretation. Dot spacing also varies between devices, so the exact angle depends on the instrument.

Depth of suppression

Plaumann and colleagues describe the Worth 4 Dot test as giving qualitative information about suppression that it cannot precisely quantify. Depth of suppression can be graded by adding neutral density filters in front of the dominant eye until the response changes. In one study of 25 people, mostly with strabismus or amblyopia, depth graded with the flashlight test and a neutral density filter bar had poor test-retest reliability (ICC 0.43). A 2026 scoping review notes that common clinical suppression tools are mainly size-based, such as the Worth 4 Dot test at varying distances, or contrast-based, such as neutral density filters.

Limits: filters, luminance and colour vision

Several factors can distort the result:

Filter quality varies. In a pilot study of 25 Worth 4 Dot boxes in one city, the green filter leaked red light in 44 of 50 test images. A quick check of the goggles is worthwhile.
The red and green dots and the room lighting can differ in brightness, which is a recognised confound.
Colour vision defects: in a retrospective chart review of 30 patients with congenital red-green colour vision defects, all 24 without strabismus or amblyopia still fused the four dots. In another small study, 5 of 32 people with colour vision defects misnamed the colours without filters, so checking colour naming first is reasonable.
The red/green filters are strongly dissociating. Earlier studies cited by Webber and colleagues reported that polarised versions reduced dissociation.

Agreement with other tests

There is no gold standard for suppression, so agreement studies compare tests with each other. In 2,280 adults, the Worth 4 Dot test and Bagolini striated lenses agreed well at distance (kappa 0.72), but the Worth 4 Dot test flagged more people with suppression. In intermittent exotropia, Worth 4 Dot results correlated only weakly with office measures of fusional control.

Digital versions are emerging. An iPad Worth 4 Dot app agreed closely with the flashlight test for fusion classification and suppression zone size in 25 participants, but its depth-of-suppression measure did not agree with other depth methods. That validation applies to that app only.

How Optics Tracker fits

Optics Tracker includes Worth 4 Dot testing as part of its alignment and sensory tests. No study above evaluated Optics Tracker's version, and their results do not apply to it.

Optics Tracker is clinical decision-support software. Its results support, and do not replace, clinical testing, professional diagnosis and clinical judgement.

Frequently asked questions

What does the Worth 4 Dot test show?

Whether the patient fuses, suppresses one eye, or has diplopia. With red/green glasses each eye sees part of a four-light target, and the number and colour of lights reported show which.

Why test Worth 4 Dot at near and distance?

The lights subtend a smaller angle at distance, so distance testing probes a more central area. Suppression at distance but not near suggests a smaller, more central suppression zone.

Can colour-blind patients do the Worth 4 Dot test?

Small studies suggest many can. In a retrospective chart review of patients with red-green colour vision defects, those without strabismus or amblyopia still fused the four dots. Another small study found some misnamed the colours, so check colour naming first.

Is the Worth 4 Dot test the gold standard for suppression?

No. There is no gold standard, and the test is mainly qualitative. In a large adult study it agreed well with Bagolini lenses at distance but flagged more people with suppression.