Worth 4 dot test
Encyclopedia
The Worth 4 dot test, also known as the Worth Lights test, is a clinical test for 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
.
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.
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
. Suppression occurs during binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
when the brain does not process the information received from either of the eyes. This is a common adaptation to strabismus
Strabismus
Strabismus is a condition in which the eyes are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscles, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision, which may adversely...
, amblyopia
Amblyopia
Amblyopia, also known as lazy eye, is a disorder of the visual system that is characterized by a vision deficiency in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities of the eye...
, and aniseikonia
Aniseikonia
Aniseikonia is an ocular condition where there is a significant difference in the perceived size of images. It can occur as an overall difference between the two eyes, or as a difference in a particular meridian.-Causes:Retinal image size is determined by many factors...
.
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
Flashlight
A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...
(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
Visual field
The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical...
. 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.