Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006

Red Filter Test

R-Esotropia ARC

Penlight

One Pink Light

FIGURE 6-11. Red filter test in a patient with a right esotropia and ARC. Red filter is placed in front of the right eye (RE) and the image falls on the pseudo-fovea (P) and fovea, representing corresponding retinal points in a patient with ARC. The patient has a single binocular perception and sees one pink light. LE, left eye.

TABLE 6-1. Types of Diplopia Tests.

Most dissociating

Maddox rod

Dark red filter

Worth 4-dot with room lights out

Worth 4-dot with room lights on

Least dissociating

Bagolini striated lenses

SPECIFIC DIPLOPIA TESTS

RED FILTER TEST

One of the simplest diplopia tests is the red filter test. Place a red glass over one eye and direct the patient to fixate on a single light source, or an accommodative fixation target. Patients with straight eyes and normal retinal correspondence will see one pinkish-red light (see Fig. 6-10). If a phoria is present, the red filter may dissociate the eyes and then the patient will manifest their deviation and see double. The denser the red color, the more dissociating the test. Another way to make the standard red filter test more dissociating is to turn down the room lights. In dim illumination, the eye behind the red filter will only see the light source, not background objects in the room, which will eliminate peripheral fusion clues. The red filter test is useful for identifying NRC, ARC, and suppression. Esotropia with NRC causes uncrossed diplopia, with the red light seen on the same side as the red filter (see Fig. 6-1). Alternately, exotropia with NRC is associated with crossed diplopia as the red light is opposite to the red filter (see Fig. 6-2). When the deviation is neutralized with a prism, the diplopia disappears and the images will be superimposed.

Patients with ARC will generally see one light, even though they have strabismus, because they use a pseudo-fovea. In Figure 6-11, the red light falls on the pseudo-fovea of the right eye. This image is cortically superimposed with the foveal image of the left eye to produce the perception of one pink light. If partial or full prism neutralization of the deviation results in diplopia, then the patient has ARC.

Strabismus associated with suppression results in the perception of a single light, either a red or a white light, depending on which eye is fixing. In Figure 6-12, the left eye is fixing, so the patient sees one white light and suppresses the red light falling on the right retina. If a dark red filter is placed over the

Red Filter Test

(Esotropia and Suppression RE)

NRC

Penlight

Red Filter

F

F

Suppression

Scotoma

Binocular

Perception

LE

One White Light

FIGURE 6-12. Red filter test in a patient with childhood esotropia who developed suppression and a fixation preference for the left eye. Patient fixes left eye with a suppression scotoma of the right eye. Note that the retinal image of the penlight falls within the suppression scotoma, so the patient only perceives one white light from the left eye.

fixing left eye, then fixation switches to the right eye, and the left eye is suppressed (Fig. 6-13). Patients who alternate fixation may report seeing two lights: a red light alternating with a white light. When a child with a manifest strabismus claims to see two

Red filter over LE

Penlight

Dark red filter

F

F

Suppression

Scotoma

Binocular

Perception

RE

One White Light

FIGURE 6-13. A dark red filter is placed over the left eye to shift fixation to the right eye. With the right eye fixing, patient suppresses the image in the left eye and perceives one white light from the right eye.

lights, be sure to distinguish between diplopia, where the red and white lights are seen simultaneously, and alternating suppression, where one light is seen at a time. Partial or full prism neutralization of the strabismus will not result in diplopia. The patient with suppression will continue to see just one light.

VERTICAL PRISM RED FILTER TEST/SUPPRESSION VERSUS ARC

Another way ARC can be distinguished from NRC in patients with suppression is by placing a red vertical prism (usually 15 PD base-down) over the deviated eye. A vertical prism causes patients with ARC to see two vertically displaced images, with the red light directly over the white light (Fig. 6-14). The lights are vertically aligned because the light in the deviated eye is over the pseudo-fovea that corresponds to the true fovea of the fixing eye.

When a vertical prism is introduced to the deviated eye of a patient with central suppression and NRC, the patient reports seeing two lights that are horizontally and vertically displaced because there is no pseudo-fovea and the center of reference is the true fovea of each eye (Fig. 6-15).

WORTH 4-DOT

The Worth 4-dot test consists of two green lights, one red light, and one white light (Fig. 6-16). The patient wears red/green glasses, usually with the red lens over the right eye, and views a Worth 4-dot flashlight at one-third of a meter, or a Worth 4- dot light box at 6 m (20 ft). The near Worth 4-dots are separated by 6° at near (flashlight at 1/3 m) and by 1.25° for the distance (light box at 6 m). When the test is performed with the room lights out, the white dot is the only binocular fusion target, as it is the only light seen by both eyes. Green lights are seen through the eye behind the green filter, and the red light is seen with the eye with the red filter. If the room lights are turned on, however, the patient can see the room environment with both eyes, including the Worth flashlight and examiner, thus providing strong fusion clues; this is why Worth 4-dot testing in the dark is much more dissociating than testing with the room lights on.

The normal fusion response is seeing four lights, two red and two green. Another normal response is one red light, two green lights and one light that flickers between red and green. The light that flickers is the white light that is seen by both

Esotropia ARC

Penlight

FP

F

F

Red prism base down

Binocular

Perception

Vertical Diplopia with

two lights in horizontal alignment

FIGURE 6-14. Patient with esotropia and ARC is presented with a basedown vertical prism and a red filter over the left eye. The prism deflects the retinal image below the pseudo-fovea (P) and the patient perceives two images: vertically, one on top of the other. Remember, the pseudofovea (P) is the center of vision during binocular viewing.

Esotropia NRC Suppression

Penlight

ET

F

F

F

Red prism base down

Binocular

Perception

Vertical and Uncrossed Diplopia

FIGURE 6-15. Patient with esotropia and suppression of left eye. A basedown prism is placed in front of the left eye, which displaces the retinal image inferiorly and out of the central scotoma. The patient perceives two images: vertically and horizontally displaced. Note that there is no pseudo-fovea (F) and the true foveas are at the center of vision.

FIGURE 6-16. Worth 4-dot test in a normal patient with straight eyes. Three lights are projected to the left eye and two lights to the right eye. Patient fuses the two images and perceives four lights.

eyes, the flicker being color rivalry. Patients with acquired strabismus and diplopia will see five lights: three green and two red. Patients with cortical suppression report seeing either three green lights or two red lights, depending on which eye is fixing. In Figure 6-9, the left eye is fixing and the right eye is suppressed so the patient sees three green lights. If the right eye was the preferred eye and the left eye was suppressed, then the patient would see two red lights. Patients who alternate fixation usually describe seeing two red lights, alternating with three green

FIGURE 6-18. Distance Worth 4-dot test in a patient with monofixation syndrome and esotropia of 8 prism diopters. The distance Worth 4-dot subtends 1.25° and two dots fall within the central suppression scotoma. Therefore, patient perceives three dots from the left eye and no dots from the right eye.

press the distance Worth 4-dot (which subtends only 1.25°) as the dots fall within the scotoma (Fig. 6-18). One of the best uses of the Worth 4-dot test is to identify the monofixation syndrome (i.e., central suppression and peripheral fusion) in a patient with a small-angle strabismus. The results of this test will tell the examiner if there is peripheral fusion that can be present even if there is no discernible stereoscopic vision.

Remember, it is important to leave the room lights on when performing the Worth 4-dot test if the goal is to promote fusion.