Chapter 12: Strabismus
List of Figures
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Figure 12-1: Ductions (monocular rotations), right eye. Arrows indicate direction of eye movement from primary position. |
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Figure 12-2: Paresis of horizontal muscle (right lateral rectus). Secondary deviation is greater than primary deviation because of Hering's law. With the left eye fixing, the right eye is deviated inward because of the paretic right lateral rectus. For the right eye to fix, the paretic right lateral rectus muscle must receive excessive stimulation. The yoke muscle, the left medial rectus, also receives the same excessive stimulation (Hering's law), which causes "overshoot," shown above. |
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Figure 12-3: Cover testing. The patient is directed to look at a target at eye level 6 m (20 feet) away. Note: In the presence of strabismus, the deviation will remain when the cover is removed. |
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Figure 12-4: Testing versions. Example of paretic left superior oblique. |
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Figure 12-5: Convergence. The position of the eyes at the normal near point of convergence (NPC) is shown above. The break point is within 5 cm of the bridge of the nose. |
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Figure 12-6: Surgical correction of strabismus (right eye). |
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Figure 12-7: Posterior fixation (Faden) procedure. The rectus muscle is tacked to the sclera far posterior to its insertion. This prevents unwrapping of the muscle as the eye turns into the muscle's field of action. The muscle is progressively weakened in its field of action. If this procedure is combined with recession, the alignment in primary position is also affected. |
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Figure 12-8: Adjustable suture. The suture is placed on the sclera at any point that will be accessible to the surgeon. The bow is untied and the position of the muscle changed as desired. |
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Figure 12-9: Incomitant strabismus (paralytic). Paralysis of right lateral rectus muscle, with left eye fixing. |
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Figure 12-10: Child with intermittent exotropia squinting in sunlight. |
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Figure 12-11: Right exotropia. |
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Figure 12-12: Right hypertropia. |
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Figure 12-13: Head tilt test (Bielschowsky test). Paresis of right superior oblique. Left: Hypertropia is minimized on tilting the head to the sound side. The right eye may then extort and the intorting superior oblique and superior rectus relax. Right: When the head is tilted to the paretic side, the intorting muscles contract together, but their vertical actions do not cancel out as usual, because of superior oblique paresis. Hypertropia is worse with head tilt to the paretic side. |
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10.1036/1535-8860.ch12