Chapter 12: Strabismus
HYPERTROPIA (Figure 12-12)
Vertical deviations are customarily named according to the high eye, regardless of which eye has the better vision and is used for fixation. Hypertropias are less common than horizontal deviations and are usually acquired after childhood.
There are many causes of hypertropia. Congenital anatomic anomalies may result in muscle attachments in abnormal locations. Occasionally, there are anomalous fibrous bands that attach to the eye. Closed head trauma may produce paresis of the superior oblique muscle. Orbital trauma or tumors, brain stem lesions, and systemic diseases such as myasthenia gravis, multiple sclerosis, and Graves' disease can all produce hypertropias. Many of these specific entities are discussed in Chapter 14.
The clinical findings may vary, depending on the cause. The history is particularly important in diagnosis of hypertropias. Prism and cover measurements in primary and cardinal positions and head tilts are the mainstay of the clinical evaluation and may often be diagnostic. Observation of ocular rotations for limitations can also be of great value.
Diplopia is almost invariably present if strabismus develops past age 6-8. As in other forms of strabismus, sensory adaptation occurs if the onset is before this age range. Suppression and anomalous retinal correspondence may be present in gaze directions where there is strabismus. In gaze directions without strabismus, there may be no suppression and normal stereopsis.
There may be head tilt, turn, or abnormal posture of the head. The deviation may be of any magnitude and usually changes with the direction of gaze. Most hypertropias are incomitant. The deviation tends to be greatest in the field of action of one of the four vertically acting muscles. There may be an associated cyclotropia, especially with superior oblique dysfunction. To measure a cyclotropia, the double Maddox rod test is used. In a trial frame, a red and white Maddox rod are aligned vertically, one over each eye. With the patient's head held straight and fixing a light, one rod is gradually turned until the observed lines are parallel to each other and to normal horizontal orientation. The angle of tilt is then read from the angular scale on the trial frame.
The superior oblique is the most commonly paretic vertical muscle. The vertical rectus muscles are commonly involved in trauma, as with entrapment of the inferior rectus in an orbital floor fracture, and in thyroid eye disease, in which the inferior rectus becomes hypertrophied, inelastic, and fibrotic, which pulls the eye downward.
Paresis of the superior oblique is usually present with hypertropia on the involved side with a head tilt to the opposite side. Other motility patterns can be seen when the deviation is of long standing, with contractures of other vertically acting muscles.
The Bielschowsky head tilt test ( Figure 12-13) is useful to confirm the diagnosis of superior oblique paresis. The test exploits the differing effects of each vertical muscle on torsion and elevation. Thus, with a paretic right superior oblique when the head is tilted to the right, the superior rectus and superior oblique contract to intort the eye and maintain the position of the retinal vertical meridian as much as possible. The superior rectus elevates the eye, and the superior oblique depresses the eye. Because of weakness of the superior oblique muscle, the vertical forces do not cancel out as they normally would, and right hypertropia increases. In head tilt to the left, the intorting muscles for the right eye relax and the inferior oblique and inferior rectus both contract to extort the eye. Both the paretic superior oblique and the superior rectus relax, and hypertropia is minimized. Hypertropia should be measured by prism plus cover with the head tilted to either side.
A. Medical Treatment:
For smaller and more comitant deviations, a prism may be all that is required. For constant diplopia, one eye may need to be occluded. Systemic disease must be treated if suspected to be the underlying cause.
B. Surgical Treatment:
Surgery is often indicated if the deviation and diplopia persist. The choice of procedure depends on quantitative measurements. The use of adjustable sutures (Figure 12-8) is frequently a great help in fine-tuning the effect of vertical muscle surgery.
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