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.

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.