Worth 4 dot test

The Worth 4 dot test, also known as the Worth dot test, is a clinical test for suppresion 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 1cm 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 16 inches (40cm), 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.