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. We could say that W4LT is one of the simpler methods for investigating fusion, suppression, and anomalous retinal correspondence (ARC).
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).
Illuminated box or flashlight (depending weather 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 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 not to forget to ask the patient, usually child a series of questions. These questions are essential and very important to every clinician:
- How many lights are you seeing?
- What color are they?
- Where are they located?
- Are all the lights in line? Or are some higher than the others?
- Do all the lights show up at one time, or are they flashing on and off?
Clinician is also advised to note the distance at which the test is conducted and whether or not the patient wore their own refractive correction. The subject should be tested with the optimal optical correction on (spectacles or contact lenses) behind the anaglyphic filters. It is also very important, when there is a difficulty in communication between clinician and patient (adult) or when working with a small children, to ask patient / child to draw what they are seeing. This simplifies a lot and helps clinician in interpretation the result from the drawing.
There are a number of possible results demonstrated by 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, suppresion 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.