The Worth 4-Dot Test
The Worth 4-dot test (Fig 7-13) is often considered a test of sensory fusion; however, it does not evaluate sensory fusion directly as there is no fusible feature in the test. Its best use is to identify a suppression scotoma. The test uses red-green glasses and a target consisting of 4 illuminated dots: 1 red, 2 green, and 1 white. By convention, the red lens is placed in front of the right eye and the green lens in front of the left. The red lens blocks the green light, and the green lens blocks the red light, so the red and green dots are each seen by only 1 eye. The white dot is the only feature seen by both eyes, but it is seen in color rivalry in a patient with fusion. The polarized Worth 4-dot test uses polarized glasses rather than red and green ones. The stimulus lights can be presented in a wall-mounted display or with a Worth 4-dot flashlight. The test should be administered in good ambient light so that peripheral features in the room can stimulate motor fusion. The patient reports the number of dots seen:
Seeing 2 dots indicates a suppression scotoma in the left eye.
Seeing 3 dots indicates a suppression scotoma in the right eye.
Seeing 4 dots indicates that if there is a suppression scotoma, it must subtend a smaller visual angle than the test target. The perception of 4 dots indicates some degree of sensory fusion, either NRC (if there is no manifest strabismus, or small-angle strabismus consistent with monofixation and peripheral fusion; see below) or harmonious ARC (if there is larger-angle manifest strabismus).
Seeing 5 dots indicates diplopia, usually from larger-angle manifest strabismus without suppression or ARC.
Figure 7-13 Worth 4-dot test. A, Looking through a pair of red-green glasses, the patient views 4 illuminated dots (1 red, 2 green, 1 white) at 6 m (projected, or mounted in a box) and at 33 cm (on a Worth 4-dot flashlight). The possible responses are given in parts B through E. B, Patient sees all 4 dots: peripheral fusion with orthophoria or strabismus with ARC. The dot in the 6 o’clock position is seen in color rivalry or, depending on ocular dominance, as predominantly red or predominantly green. C, Patient sees 2 red dots: suppression in left eye. D, Patient sees 3 green dots: suppression in right eye. E, Patient sees 5 dots: uncrossed diplopia with esotropia if the red dots appear to the right of the green dots, as in this figure; crossed diplopia with exotropia if the red dots appear to the left.
(Modified with permission from von Noorden GK, Campos EC. Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th ed. St Louis: Mosby; 2002:221.)
In monofixation syndrome (see Chapter 5), the Worth 4-dot test can demonstrate both the presence of peripheral fusion and the absence of bifixation. The standard Worth 4-dot flashlight projects onto a central retinal area of 1° or less when viewed at 3 m (10 ft), well within the 1°–4° scotoma characteristic of monofixation syndrome, so patients with monofixation syndrome report seeing 2 or 3 lights, depending on fixation preference. As the Worth 4-dot flashlight is brought closer to the patient, the dots project onto more peripheral retina outside the central monofixation scotoma and a fusion response (4 lights) is obtained. This usually occurs between 0.67 and 1 m (2–3 ft).
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.