| Worth 4 dot test | |
|---|---|
 Worth Four Light Test | |
| Synonyms | W4LT |
| Purpose | assess degree of binocular vision |
The Worth Four Light Test, also known as the Worth's four dot test or W4LT, is a clinical test mainly used for assessing a patient's degree of binocular vision and binocular single vision. Binocular vision involves an image being projected by each eye simultaneously into an area in space and being fused into a single image. The Worth Four Light Test is also used in detection of 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.
The W4LT can be performed by the examiner at two distances, at near (at 33 cm from the patient) and at far (at 6 m from the patient). At both testing distances the patient is required to wear red-green goggles (with one red lens over one eye, usually the right, and one green lens over the left) When performing the test at far (distance) the W4LT instrument is composed of a silver box (mounted on the wall in front of the patient), which has four lights inside it. The lights are arranged in a diamond formation, with a red light at the top, two green lights at either side (left and right) and a white light at the bottom. When performing the test at near (at 33 cm ) the lights are arranged in exactly the same manner (diamond formation), with the difference being that at near, the lights are located in a hand-held instrument which is similar to a light torch.
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 and 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 (diplopia).