Figure 7-15 Worth 4-dot test. A, Looking through a pair of red-green glasses, the patient views a box with 4 lights (1 red, 2 green, 1 white) at 6 m and at 33 cm (with the 4 lights mounted on a flashlight). The possible responses are given in parts B to E. B, Patient sees all 4 lights: Peripheral fusion with orthophoria or strabismus with ARC. The light 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 lights: Suppression in left eye. D, Patient sees 3 green lights: Suppression in right eye. E, Patient sees 5 lights: Uncrossed diplopia with esotropia if the red lights appear to the right of the green lights, as in this figure; crossed diplopia with exotropia if

the red lights 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 6), the Worth 4-dot test can be used to 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. Therefore, patients with monofixation syndrome will report seeing 2 or 3 lights, depending on their ocular 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 m and 1 m (2–3 ft).

Stereoacuity Testing

Stereopsis occurs when the 2 retinal images—which have small disparities due to the horizontal separation of the eyes—are cortically integrated. There are 2 types of stereopsis tests: contour and random dot. Contour stereopsis tests involve horizontal separation of physical contours presented to each eye (with polarized or red-green glasses). At larger disparities, monocular cues are present in this type of test. Random-dot stereopsis tests avoid the problem of monocular cue artifacts by embedding the stereoscopic figures in a background of random dots.

In the Stereo Fly test (a contour stereopsis test), a card with superimposed images of a fly is shown to the patient. Ability to detect the elevation of the fly’s wings above the plane of the card indicates stereopsis. Because the separation of the superimposed images is 3000 seconds of arc, this test is one of gross stereopsis. In other figures on the card, there is less separation between the superimposed images. Thus, quantitation of finer stereoacuity is possible in cooperative patients.

Several types of random-dot stereopsis tests are clinically useful. The Randot test, in which polarized glasses are worn, can measure stereoacuity down to 20 seconds of arc. The Random-Dot E test employs a preferential looking strategy to test stereopsis and is used in pediatric vision screening programs. In the TNO test, red-green glasses are used to separate the images seen by each eye. The Lang stereopsis tests do not require glasses to produce a random-dot stereoscopic effect and therefore may be useful in young children who object to wearing glasses.

Stereopsis can also be measured at distance using a chart projector with a vectographic slide, the Smart System PC-Plus (M&S Technologies, Niles, IL) or the Frisby Davis Distance Stereotest (Stereotest Ltd, Sheffield, United Kingdom). Distance stereoacuity tests may be helpful in monitoring control of intermittent exotropia.

Related Videos

The following videos contain additional information on topics covered in this chapter and are available at https://aao-resources-enformehosting.s3.amazonaws.com/resources/AAO.LMS/BCSC151 6/section6.html.