Introduction  

The Worth 4 Dot test is an eye exam used to assess the patient's binocular vision and single binocular vision. It is also used to detect suppression. The test is among the more straightforward techniques for testing fusion, anomalous retinal correspondence and suppression. Claude Worth introduced the analysis in 1903 for measuring binocularity. In 1937, Hardy integrated the lights into a flashlight, and several doctors subsequently made further modifications. The Worth 4 dot test has become the standard test for sensory function in the abnormal alignment of the eyes (strabismus).
 

Also Known As

  • W4LT
  • Worth Four Dot Test
  • Worth Four Light Test

 

Purpose

The test can be conducted at the doctor's office or eye clinic by:

  • An optometrist
  • An ophthalmologist

 

The specialist can use the test to develop, support, or verify an initial diagnosis. 

Despite the advances in techniques and equipment over the last 120 years, the W4LT has remained an invaluable test for evaluating acquired and long-standing strabismus in adults. It is also useful in the management of complex diplopia (double vision). 

The doctor can use the test to assess binocular functions and the ability of the patient's eyes to coordinate or work together. S/he can use it to investigate a patient's binocular single vision response, i.e., determine whether it's healthy or abnormal. The test is also helpful in determining if a patient has double vision or suppression. Suppression is a disorder in which the brain ignores or subdues signals from one of the eyes to compensate for visual difficulties. 

Where the patient has manifest strabismus, W4LT can help the doctor to establish the eye that is suppressing images or the type and nature of the diplopia. Furthermore, the test may help in determining the patient's dominant eye and for evaluating decreased monocular visual acuity. 

In some cases, the doctor may have to combine the Worth Four Dot test with additional clinical tests such as the cover test, for a final diagnosis.
 

Preparation & Expectation

There is no special preparation required for the Worth Four Dot test.
 

Procedure 

The doctor can conduct the test at two distances, at 33 centimeters (near) and 6 meters (distant) from the patient.

The patient can stand or sit on a stool or chair in a room with dim lighting. The doctor will place green/red shades over the patient's eyes. Usually, the red shade covers the right eye while the green one covers the left eye.

For the distant test, the doctor will use a silver box with four lights inside. It will be mounted on the wall ahead of the patient. The lights will be in a rhombus shape, the red light at the top, the white light at the bottom and two green lights on either side. For the near test, the doctor will use Worth's Four Lights torch, which is a hand-held device similar to an ordinary light torch fitted with the four lights in the same formation (rhombus shape).

In both tests, the patient will look at the lights through the goggles and answer a series of questions. The doctor will record the patient's answers, interpret the results and make a diagnosis.
 

Outcome

There are several possible outcomes demonstrated by the Worth Four Dot test:

Normal retinal correspondence

The patient sees the lights as they appear: 

Four lights; one red, two green and one mixed color
The red light slightly above, the two green lights on either side and the mixed colored light below the red

Abnormal retinal correspondence

The cover test will demonstrate that the patient has a manifest deviation. However, the patient will report seeing the lights precisely as they appear. 

  • Suppression

There is suppression if the patient reports seeing:

Two red lights or three green lights (Alternating suppression)
Only the two red lights from the right eye (Left suppression)
Only the three green lights from the left eye (Right suppression)

  • Esotropia

The patient will experience uncrossed diplopia. They will report seeing:

Five lights, two red and three green
The lights appearing side by side, horizontally displaced
The two red lights from the right eye on the right side
The three green lights from the left side on the left eye 

  • Exotropia

The patient will have crossed diplopia. They will report seeing:

Five lights, two red and three green
The lights side by side, horizontally displaced
The two red lights from the right eye on the left side
The three green lights from the left eye on the right side

  • Hypotropia/Hypertropia

Where the patient has vertical deviations, they will report seeing:

Five lights, two red and three green
The lights vertically displaced to one another
The green lights on top of the red lights, or
The red lights on top of the green lights
 

Risks & Complications

The Worth 4 Dot test is a non-contact and non-invasive examination without risks.