Worth 4 dot
The Worth Four Light Test, also known as the Worth's Four Dot test or abbreviation W4LT, is one simple clinical test mainly used for assessing a patient's degree of binocular vision. It would be fair to say that W4LT is one of the simpler methods for investigating fusion, suppression, and anomalous retinal correspondence (ARC) and can be easily performed on very young patients.
This test can be performed in two methods (ways). One method is to have a fixed target at a distance from the subject, which may either be contained in an illuminated box or projected on a screen. This is referred to as the distant Worth dot test (6 meter) . The other method is a near Worth dot test (at 33 cm), which consists of a flashlight easily advanced or receded from the subject to alter the projection angle of the target image on the retinas. At both testing distances (distance and near) the patient is always required to wear red-green goggles (with one red lens over one eye, usually the right, and one green lens over the left).
The illuminated box or flashlight (depending on whether the test is performed at distance or near) is composed of 4 lights, which are arranged in a diamond formation. One red light is always at the top, two green lights are located at either side (left and right) and one white light is always at the bottom. The patient views the target through anaglyphic testing glasses that consist of a red filter in front of one eye and a green filter in front of the other. Viewed through the red filter, the green dots are invisible; viewed through the green filter, the red dot is invisible. The white dot is seen as red when viewed through the red filter and as green when viewed through the green filter.
Interpretation of Worth Four Light test
Before the doctor starts to perform interpretation of worth four light test, it is very important to ask the patient, usually a child, a series of questions. These questions can help orient the child to the test, and help provide valid responses:
- How many lights are you seeing?
- What color are they?
- Where are they located? (Often asking a child to touch the lights they see for near testing can confirm their verbal responses)
- Are all the lights in a line? Are some higher than the others?
- Do all the lights show up at one time, or are they flashing on and off?
Clinicians should also be advised to note the distance at which the test is conducted, and whether or not the patient wore their own refractive correction. Ideally, patients should be tested with their optimal optical correction (spectacles or contact lenses) behind the anaglyphic filters. In cases where there is difficulty in communication between the clinician and patient, ask the patient to draw what they are seeing.
There are a number of possible results from a W4LT
The patient sees all four dots :
- Normal binocular response with no manifest deviation (NRC with no heterotropia)
- Harmonious ARC with manifest squint
The patient sees five dots:
- Uncrossed diplopia with esotropia, red dots appear to the right
- Crossed diplopia with exotropia, red dots appear to the left of the green dots
The patients sees three green dots, suppression of the right eye
The patient sees two red dots, suppression of the left eye
- Worth C. Squint: Its causes, pathology and treatment. Philadelphia: Blakiston, 1908
- Noorden GK von. Binocular vision and ocular motility: theory and managment of strabismus, 5th Ed. St Louis: Mosby, 1996.
- Duane’s Clinical Ophthalmology. New York: Lippincott Williams & Wilkins, 2005.