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

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FIGURE 5-3A,B. (A) Versions showing overaction of the oblique muscles: upper drawing, right inferior oblique overaction 3; lower drawing, right superior oblique overaction 3. (B) Versions showing underaction of the oblique muscles: upper drawing, 3 underaction of the right inferior oblique; lower drawing, 3 underaction of the right superior oblique.

looking around the occluder to see if the eye manifests the oblique dysfunction (Fig. 5-4).

Measuring Ocular Deviation

The methods for measuring the angle of strabismus have been divided into the following categories: light reflex tests, cover tests, and subjective tests. Light reflex tests are the easiest to perform on young children and infants. These tests, however, are not as precise as other tests such as the cover tests. The Lancaster red-green test is useful in adult patients with diplopia and an incomitant deviation.

Most methods for measuring ocular deviations involve prisms. There is a basic discussion on the use of prisms in stra-

FIGURE 5-4. Versions showing an occluder is placed in front of the right eye to ensure that the patient fixates with the left eye. When patient is fixing left eye, it allows the inferior oblique overaction to become obvious and manifest. If the patient were to fix with the right eye, however, one would not see a downshoot because of Hering’s law.

bismus in Chapter 3. For prism neutralization of a deviation, remember to orient the prism so the apex points in the same direction as the deviated eye. Esotropia is corrected with a baseout prism, exotropia with a base-in prism, and hypertropia by a base-down prism.

When measuring a deviation, it is critical that the patient is fixating and appropriately accommodating on the fixation target. Accurate measurements cannot be obtained if the patient is gazing around the room or daydreaming and not accommodating on the fixation target. An accommodative target is a target that has fine detail that requires accurate accommodation to be seen. A penlight, for example, is a poor accommodative target as there is no fine detail and accommodation is not required to see the light. One of the best accommodative targets for adults, in the distance or near, is Snellen letters at a size close to visual threshold. By having the patient read the letters, the examiner knows that the patient is accommodating on the fixation target. For young children, small detailed toys or small pictures with

fine detail can be used at near and a children’s video or animated toys in the distance.

LIGHT REFLEX TESTS

HIRSCHBERG TEST

The Hirschberg test, or corneal light reflex test, assesses eye alignment by the noting the location of the corneal light reflex within the pupil. The term corneal light reflex is a misnomer, as it is not a reflex off the cornea. What we perceive as the light reflex is actually the first Purkinje image, which is a virtual

image located behind the pupil. The Hirschberg test should be performed by holding a light source (muscle light or penlight) in front of the examiner’s eye and directing the light into the patient’s eyes. Have the patient look at the light, then assess the location of the light reflex in each eye. Hirschberg testing is only valid if the patient fixes on the light source. The examiner must view the light reflexes from a position directly behind the light source. Therefore, for practical purposes, the Hirschberg test can only be performed at near. An accommodative fixation target can be placed next to the light source to attract the patient’s attention and provide an accommodative target.

With normal orthotropic alignment, the light reflexes are slightly decentered nasally, but they are symmetrically located within each pupil. Slight symmetrical nasal displacement of approximately 5° is normal and is a “physiological” positive angle kappa (see Angle Kappa, below). Patients with strabismus will have an eccentric light reflex in the deviated eye. Temporal displacement of the light reflex indicates esotropia, nasal displacement indicates exotropia, and inferior displacement indicates hypertropia (Fig. 5-5). One can estimate the size of an ocular deviation by the amount of light reflex displacement within the pupil. Temporal displacement of the light reflex to the pupillary margin indicates an esotropia of 15° (ET 30 PD), displacement to the temporal midiris indicates esotropia 30° (ET 60 PD), and temporal displacement to the limbus indicates an esotropia of 40° (ET 80 PD). Another way to estimate the angle of deviation is to multiply the millimeters of light displacement by 15 PD to give the deviation in prism diopters.3,6,7 Thus, 2 mm of nasal displacement of the reflex from its normal location when viewing monocularly indicates an exotropia of 30 PD. These are relatively gross estimates and, as a rule, are not used to determine the amount of surgery.

ANGLE KAPPA

Angle kappa measures the angle between the line of sight and the corneal–pupillary axis. The line of sight is a line from the fixation target to the fovea, and the corneal–pupillary axis is a line from the center of the pupil that is tangential to the cornea. Angle kappa is a monocular measurement of monocular alignment to a visual target. Angle kappa does not have any relationship to the fellow eye and does not measure strabismus. If the fovea is located directly behind the pupil, then the line of sight would be in line with the corneal–pupillary axis and the

FIGURE 5-5. Hirschberg test: top drawing, normally centered reflex; second drawing, esotropia, right eye, with the light reflex deviated temporally; third drawing, exotropia, right eye, with the light reflex deviated nasally; bottom drawing, right hypertropia, with the light reflex deviated inferiorly.

angle kappa would be 0°. On the other hand, a fovea located off center (not directly behind the cornea) creates a discrepancy between the line of sight and the corneal–pupillary axis, resulting in an angle kappa (Fig. 5-6). A positive angle kappa is associated with a temporally displaced fovea (Fig. 5-6A). With the fovea displaced temporally, the eye must abduct to put the image on the fovea, which causes a nasal displacement of the Hirschberg light reflex and gives an exo-appearance. Figure 5-7A shows a patient with a positive angle kappa, left eye, caused by a dragged left macula secondary to retinopathy of prematurity. This patient appears to have an exotropia but is actually orthotropic. When the left eye is covered, the right eye remains

Most normal patients have a physiological positive angle kappa, as the fovea is located 5° temporal to the center of the posterior pole; this is why we usually see the Hirschberg light reflex as being slightly decentered nasally in orthotropic patients. An angle kappa can be distinguished from a tropia by the cover/uncover test (see following). If the light reflex is displaced from the center of the pupil with monocular viewing, this indicates an abnormal angle kappa, not strabismus (Fig. 5-7B).

KRIMSKY TEST

The Krimsky test adds use of a prism to the Hirschberg test to measure a strabismus. This test is indicated to estimate the deviation size in uncooperative patients and patients with sensory strabismus and poor vision of 20/400 or worse. A prism is placed in front of one eye, with the base oriented appropriately (esotropia, base-out; exotropia, base-in; hypertropia, base-down) to neutralize the deviation. A penlight is then shone into both eyes as described for the Hirschberg test. The patient is directed to fixate on an accommodative target juxtaposed to the penlight. The prism is increased or decreased until the reflex from each eye becomes equally and symmetrically centered in the pupil. Placing a prism over the fixing eye in a patient with a tropia will cause a version movement in which both eyes move in the direction of the apex of the prism, which moves the light reflex in the deviated eye (Fig. 5-8). Placing the prism over the nonfixing eye directly moves the light reflex to the center of the pupil without a version shift. One can place the prism over either eye, except in cases of a restriction or paresis. In these patients, measure the primary deviation by placing the prism over the eye with limited rotations and mesure the secondary deviation by placing the prism over the eye with full ductions (see primary versus secondary deviation, following).

BRÜCKNER REFLEX TEST

The Brückner reflex test is performed by using the direct ophthalmoscope to obtain a red reflex from both eyes simultaneously. Make sure that the patient is looking at the light during the Brückner test; if the patient looks to peripheral targets, the test is invalid. In patients with strabismus, the Brückner test will show asymmetrical reflexes with a brighter reflex coming from the deviated eye. There is less pigment in the peripheral retina, so the deviated eye will reflect more light. This is a screening test that identifies strabismus and pathology that

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FIGURE 5-8A,B. The Krimsky test in a patient with esotropia. (A) The light reflex is deviated temporally in the esotropic left eye. (B) A base-out prism is presented in front of the right eye, which is fixing. The patient continues to fixate with the right eye, but the right eye turns in to pick up fixation. The left eye, because of Hering’s law, moves temporally. The left eye is now centered and the right eye is turned in; however, the light reflex would be centered in both eyes; this is the neutralization point, and the amount of prism needed to achieve the neutralization point measures the angle of deviation.

change the normal red reflex including anisometropia, gross retinal pathology, large retinal detachment, and corneal, lenticular, or vitreous opacities (see Chapter 4; Figs. 4-13, 4-14).

COVER TESTS

COVER/UNCOVER TEST

The cover/uncover test is designed to detect the presence of a tropia in patients who appear to have straight eyes and may be fusing. The idea is to test for a tropia without dissociating an existing phoria. Cover/uncover testing is performed by very briefly covering the eye that is thought to be the fixing eye while observing the eye suspected of deviating for a tropia shifts as the eye picks up fixation. If there is no shift, then perform cover/uncover testing on the opposite eye. If there is no shift of either eye after covering and uncovering each eye, then there is no manifest tropia and the eyes are straight, that is, orthotropia. If briefly covering one eye produces a refixation shift of the fellow eye, then a manifest tropia is present. A nasal to tempo-

ral refixation movement indicates an esotropia, a temporal to nasal shift indicates an exotropia, and a downward shift indicates a hypertropia (Fig. 5-9).

Be sure to have the patient fixate on an accommodative target during testing, as the test is invalid if fixation is uncontrolled and wandering. Cover the fixing eye for 1 to 2 s, just long enough to see if there is a shift of the uncovered eye to midline. The cover/uncover test can be dissociating and can manifest an underlying phoria if the test is performed improperly by covering one eye for several seconds. Prolonged occlusion of one eye will break up fusion, and the patient will manifest a phoria that may erroneously be called a tropia because it is associated with the cover test. Remember to briefly cover one eye for only 1 or

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FIGURE 5-9A–C. Cover/uncover test. (A) Esotropia. Left eye is fixing. When the left eye is covered, the right eye moves out to pick up fixation. This outward movement indicates that the right eye is esotropic. (B) Exotropia. Left eye is fixing. When the left eye is covered, the right eye turns in to pick up fixation. The inward movement indicates that the right eye is exotropic. (C) Right hypertropia. Left eye is fixing. Covering the left eye causes the right eye to come down to pick up fixation. Movement of the right eye indicates a right hypertropia.