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

FIGURE 6-19A–E. Patient perception of Bagolini testing. (A) A cross is perceived in orthotropia with normal retinal correspondence or strabismus with ARC. (B) Patient with strabismus and large suppression scotoma sees one line. (C) Patient with monofixation syndrome and small central scotoma will see one continuous line and one line broken in the center that corresponds to the eye with the suppression scotoma. (D) Patient with esotropia and uncrossed diplopia reports a “V” configuration. (E) Patient with exotropia and crossed diplopia reports an “A” configuration.

pseudo-fovea (see Fig. 6-7). Patients who have large regional suppression will report seeing only one line (Fig. 6-19B). The monofixation syndrome, on the other hand, is associated with a cross, but one line will have a central gap (Figs. 6-19C, 6-5). Patients with NRC, heterophoria, and diplopia will show the response of either an “A” or a “V.” Because esotropia is associated with uncrossed diplopia, esotropia will cause the right line to move to the right and the left line to move to the left, creating a “V” (Fig. 6-19D). Exotropia produces an “A” because exotropia is associated with crossed diplopia, with the right line moving to the left and the left line moving to the right (Fig. 6-19E).

MADDOX ROD TEST

The Maddox rod can be used for identifying horizontal, vertical, and, especially, torsional deviations. The Maddox rod has a washboard appearance as it is made up of multiple cylindrical high plus lenses stacked on top of each other. When the patient views a light through the Maddox rod, a linear streak of light oriented 90° to the cylindrical ribs of the Maddox rod is seen. The single Maddox rod test is performed by placing the Maddox rod over one eye and having the patient view a penlight. The Maddox rod is aligned so the streak is vertical to detect horizontal deviations and then horizontal for vertical deviations. If the streak of light passes through the penlight, the patient is orthophoric, or has harmonious ARC. This is one of the most dissociating tests, because the images to each eye are totally different and there are essentially no binocular fusion clues. The Maddox rod test is so dissociating that it will cause patients with normal bifoveal fusion to manifest their phoria. Because of this, the Maddox rod test, and dissociating tests in general, do not distinguish between phorias and tropias. To make the diagnosis of phoria versus tropia, one must assess the eye alignment objectively before administering the dissociating diplopia test. The Maddox rod test can also be used to measure torsion (as described in Chapter 5).

Haploscopic Tests

In contrast to diplopia tests where there is one stationary fixation target that is viewed by both eyes, haploscopic tests have two fixation targets, one for each eye, and the targets can be moved separately to align with each fovea. A haploscopic presentation means each eye receives its own visual stimulus. There are various ways to separately stimulate each eye. One way to create haploscopic vision is to place a mirror in front of each eye, with the mirrors angled so the right eye sees the right temporal side and the left eye sees the left temporal side. Mirror separation of vision is the principle of the amblyoscope. Another commonly used method is to give the patient color-tinted glasses with one eye receiving a red filter and the fellow eye a green filter. Two movable targets are presented on a white screen: one red and one green. The eye with the red filter sees only the red target and the eye with the green filter sees only the green target; thus, separate visual stimuli are presented to each eye; this is the principle of the Lancaster red/green test. If

FIGURE 6-22. Patient with harmonious ARC and right esotropia. The arms of the amblyoscope do not have to be angled for the patient to see the dot inside the ring, as the pseudo-fovea (P) is directly aligned with the ring target. The patient perceives the dot in the center of the circle with the arms of the amblyoscope parallel aligned to zero.

ANOMALOUS RETINAL CORRESPONDENCE (HARMONIOUS)

Patients with strabismus and harmonious ARC have a significant objective angle, but the subjective angle is zero. The subjective angle is zero (or close to zero) because the subjective angle is measured under binocular conditions and reflects the alignment based on the relationship between the true fovea of the fixing eye and the pseudo-fovea of the deviated eye. Because patients with harmonious ARC have the pseudo-fovea positioned to compensate for the angle of deviation, there is no subjective misalignment. Patients with harmonious ARC will see the targets from each eye as superimposed with the amblyoscope arms set to zero (parallel) even though there is a large objective angle (Fig. 6-22). The objective angle is measured by alternate cover testing, blocking the vision of each eye (monocular viewing) so the objective angle reflects the misalignment based on the true fovea. The displacement of the pseudo-fovea off the true fovea is called the angle of anomaly. Because the location

the fixing eye is on the true fovea, and the image in the nonfixing eye is on the pseudo-fovea. The subjective angle is the number of degrees from the zero position the amblyoscope arm needs to move to place the image on the pseudo-fovea. For example, in Figure 6-23, the subjective angle (I-P, right eye) is 10 PD, and the objective angle (I-F, right eye) is 30 PD. Because the angle of anomaly (P-F) is equal to the objective angle minus the subjective angle, the angle of anomaly is 20 PD (30 10).

The amblyoscope is a useful tool as it can measure fusional vergence amplitudes, angle of deviation, area of suppression, retinal correspondence, and even torsion. Some degree of instrument convergence, however, is usually present when using the amblyoscope.

AFTERIMAGE TEST

The afterimage test is a fovea-to-fovea sensory test that does not use a haploscopic apparatus, but each eye is stimulated separately. Each fovea is marked individually during monocular viewing with a linear strobe light that bleaches the retina; this causes a linear afterimage shadow through the true fovea that lasts approximately 10 s. The center of the linear strobe light is masked to spare the fovea; thus, the afterimage line has a break in the middle. Testing is performed by having the patient occlude one eye while the other eye fixates on the central masked part of the strobe light held vertically in front of the patient (Fig. 6-24). The fixing eye is stimulated to produce a vertical afterimage. Next, the fellow eye is stimulated with a horizontally oriented strobe light while the first eye is covered (Fig. 6-24B). The occluder is quickly removed, and the patient is asked where they see the afterimage lines while they are binocularly viewing (Fig. 6-24C). Because the stimulus is presented under monocular conditions, the stimulus always marks the true fovea of each eye unless there is eccentric fixation from dense amblyopia. Patients with NRC will, therefore, always see a cross whether they are orthophoric, esotropic, exotropic, or hypertropic because their center of reference is the fovea under monocular or binocular conditions (Fig. 6-25A,B). Patients with ARC however, use their true fovea during monocular viewing but, during binocular viewing, the deviated eye switches to the pseudo-fovea. Consequently, patients with ARC have each fovea marked by the monocular afterimage, but when binocular vision is reestablished, the pseudo-fovea takes over as the center of