Worth 4 dot test

Worth 4 dot test

The Worth 4 dot test, also known as the Worth Lights test, is a clinical test for suppression of either the right or left eye. Suppression occurs during binocular vision when the brain does not process the information received from either of the eyes. This is a common adaptation to strabismus, amblyopia, and aniseikonia. During the Worth 4 dot test, the patient, wears anaglyphic glasses (with one red lens over one eye, usually the right, and one green lens over the other eye, usually the left). The patient is shown a modified flashlight (torch) with four holes, approximately 1 cm in diameter, organized in a diamond shape. Traditionally, the holes are arranged with the top hole showing only red light, the left and right showing only green light, and the bottom showing white light.

Because the red filter blocks the green light and the green filter blocks the red light, it is possible to determine if the patient is using both eyes simultaneously in a coordinated manner. With both eyes open, a patient with normal binocular vision will appreciate four lights. If the patient either closes or suppresses an eye they will see either two or three lights. If the patient does not fuse the images of the two eyes, they will see five lights.

The testing distance can be varied to assess the size the area of suppression of the patient's visual field. If the flashlight is held at 33 cm, the lights appear larger and tests for a large area of suppression. If the flashlight is held at a greater distance (traditionally 10 feet or 3 metres), a smaller area is tested.

Recording and Interpreting outcomes

When recording results for the W4LT it is important to ask the patient a series of questions in order to ensure you correctly record exactly what they are seeing. This is essential in order to interpret the patient’s results and then make an accurate diagnosis.

The questions are:

1. How many lights are you seeing?
2. What colour are they? Where are they located?
3. Are all the lights in line? Or are some higher than the others?
4. Do all the lights show up at one time, or are they flashing on and off?

When recording results it is important to indicate the test used, a description of the lights seen and an indication of what the result means. It is also important to note the distance at which the test was conducted and whether or not the patient wore their own refractive correction.

Where communication is difficult between clinician and patient, such as in the presence of a language barrier, or when working with a child, it may be a good idea to get the patient to draw what they are seeing. The clinician can then interpret the results from the image.

Results

There are a number of possible results demonstrated by a W4LT

Normal retinal correspondence

In the absence of a deviation, the patient will see the lights exactly as they appear. When questioned they will report that:

• They see 4 lights, 1 red, 2 green and one mixed colour
• The two green lights will be to either side with the red light slightly above them and the mixed coloured light below the red

This is recorded as : W4LT (D): 4 lights (BSV)

Abnormal Retinal Correspondence

It will be demonstrated on cover test that the patient has a manifest deviation. When questioned about the lights the patient will illicit a normal response and will see the lights exactly as they appear. They will report that:

• They see 4 lights, 1 red, 2 green and one mixed colour
• The two green lights will be to either side with the red light slightly above them and the mixed coloured light below the red

This is recorded as : W4LT (D): 4 lights (ARC)

NB: ARC can only be confirmed in conjunction with additional clinical tests for retinal correspondence. The patient must demonstrate a manifest deviation on cover test. Despite their apparent deviation, when tested with the W4LT they will produce a normal BSV result, indicating the presence of Abnormal Retinal Correspondence.

Esotropia

In an Esotropic (ET) deviation, the patient will experience uncrossed diplopia. When questioned about the position of the lights, they will report that:

• They see 5 lights, 2 red and 3 green
• The lights are horizontally displaced, seen side by side
• The 2 red lights from the right eye are seen on the right side
• The 3 green lights from the left eye are seen on the left side

This is recorded as: W4LT (D): 5 lights (Uncrossed Diplopia) ET

NB: The clinician will be unable to indicate which eye is the deviating eye based on these results alone. The results should be interpreted with other clinical findings in order to produce a final diagnosis.

Exotropia

In an Exotropic (XT) deviation, the patient will experience crossed diplopia.

When questioned about the position of the lights, they will report that:

• They see 5 lights, 2 Red and 3 Green
• The lights are horizontally displaced, and are seen side by side
• The 2 Red Lights from the Right eye are on the left side
• The 3 Green lights from the Left eye are on the right side

This is recorded as: W4LT (D): 5 lights (Crossed Diplopia) XT

NB: The clinician will be unable to indicate which eye is the deviating eye based on these results alone. The results should be interpreted with other clinical findings in order to produce a final diagnosis.

Hypotropia/Hypertropia

In cases of vertical deviations, patients will report that:

• They see 5 Lights, 2 Red and 3 Green
• The lights are vertically displaced in relation to one another
• The Green lights (Left eye) are on top of the Red lights (Right eye)

Which is interpreted as : R HypoT or LHT

• The Red lights (Right eye) are on top of the Green lights (Left eye)

Which is interpreted as: RHT or L HypoT

This is recorded as: W4LT (D): 5 lights (Vertical Diplopia)

The clinician can relate the position of the lights directly back to the deviation and height of the eye (ie) the higher lights belong to the higher eye, and the lower lights belong to the lower eye

NB: If the lights are not situated directly above one another, but are also separated horizontally, it is normally indicative of a mixed deviation where there is a horizontal, as well as vertical strabismus present

Suppression

In cases of manifest strabismus, it is not always expected that the patient will experience diplopia.

Suppression is indicated when the patient reports that:

• They see only the 3 Green lights from the Left eye

Which is interpreted as R Suppression

• They see only the 2 Red lights from the Right eye

Which is interpreted as L Suppression

• They see 2 Red lights OR 3 Green lights

All 5 lights are never present at the same time, but the patient is switching between the two responses. This result is interpreted as Alternating Suppression

This can be recorded as:

W4LT (D): 2 Lights (L Supp.)

W4LT (D): 3 Lights (R Supp.)

W4LT (D): 2 or 3 Lights (Alt. Supp.)

See also

• Eye examination
• Diplopia

References

• Eskridge, JB, Amos, JF, Bartlett, JD. Clinical procedures in Optometry. Lippincott Co. New York 1991.
• Carlson, NB, et al. Clinical Procedures for Ocular Examination. Second Ed. Mc Graw-Hill. New York 1996.
• Madge, SN, Kersey, JW, Hawker, MJ, Lamont, M. Clinical Techniques in Ophthalmology. Churchill Livingstone. London 2006
• Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. DOI: 10.1002/9780470698839