Vertical strabismus

Motilty exam

Before measuring the deviation, observe whether the patient has a spontaneous compensatory head posture (CHP) with visual effort. Although there are many causes for CHPs, this author finds they mostly serve to place the eyes in a gaze field in which the deviation is less, or to damp nystagmus (see Chapters 83 and 90 ). The presence of facial asymmetry typically identifies the CHP as dating back to early childhood. There is a shortening of the midface between the horizontal canthus laterally and the corner of the child's mouth on the side to which the head is habitually tilted ( Fig. 82.1 ). Measure the deviation with the head posture using the prism and alternate cover test, and then in the head-erect position. Although a diagnosis can often be made by just measuring a patient in seven fields of gaze (primary, up, down, right, and left) and on head tilt right and left, an optimum treatment plan often requires additional measurements in the four oblique fields. Ductions and versions should be assessed with particular attention to the presence of overelevation or overdepression in the oblique fields. If there is overelevation of the adducting eye on side gaze, do a cover test in that gaze field to ascertain if the vertical deviation is a manifestation of DVD or true inferior oblique overaction. In Video 82.1 both boys show overelevation of either eye in adduction. The first boy does not have a hypotropia of the abducting eye when cover testing is done in side gaze. His overelevation in adduction is solely due to DVD. The second boy does have a significant hypotropia of the abducting eye when cover testing is done in side gaze. He has DVD coexisting with true inferior oblique overaction.

Determine if the deviation is dissociated or not. With a non-dissociated deviation, a hypotropia is present in the contralateral eye when fixation is with the higher eye. Unless a secondary deviation is present due to paresis or restriction, the hypotropia in one eye will be of equal size to the hypertropia of the other eye. With DVD, the hypotropia of the fellow eye is either smaller or absent when fixation is with the eye with the DVD (see below “Dissociated vertical divergence”).

The Parks' three-step test will tell, in theory, which of the eight cyclovertical muscles is paretic; however, in practice it works best for confirming the diagnosis of unilateral superior oblique palsy. Even in cases of isolated superior or inferior rectus palsy, it may be misleading. Most importantly, it does not tell whether a vertical strabismus is due to a palsy of one of the cyclovertical muscles, but is based on the assumption that it is. Box 82.1 lists some of the common situations in which the three-step test leads to an incorrect diagnosis. The man in Video 82.2 developed vertical diplopia immediately after closed head trauma from a motor vehicle accident. He had a left hypertropia that increased in right gaze and on left head tilt, thus meeting the three-step test criteria for a left superior oblique palsy. In fact, he had an orbital floor fracture in his right eye. He consistently fixed with his right eye due to mild amblyopia in his left eye. His diplopia resolved when the fracture was repaired.

You should test for the presence of torsion, both objectively and subjectively. The latter is accomplished with the double Maddox rod test using two red lenses, because the use of one red and one white lens frequently leads to a localization artifact; if the eye behind the white lens is the one that is torted, the patient will frequently perceive the torsion as being in the eye behind the red lens. However, in my practice even when I use two red lenses, I sometimes find that the double Maddox rod test just reveals the total amount of torsion between the two eyes, and may be misleading with respect to localizing to the specific eye affected. Objective torsion is determined with the indirect ophthalmoscope and may be more useful in determining which eye actually is torted. Normally the position of the fovea should be level with the lower one-third of the optic disc ( Fig. 82.2 ). The absence of subjective torsion in the presence of objective fundus torsion usually means the deviation is longstanding and sensory adaptations have occurred. If a patient describes torsion, determine if the patient can fuse when the vertical and horizontal deviations are corrected with prisms. If the patient can fuse comfortably despite the presence of torsion, it may be possible to ignore the torsion when designing a surgical strategy. If they cannot fuse, there may be a central disruption of fusion. Testing on the synoptophore, which can also correct the torsion, may determine whether one can expect fusion if the strabismus is successfully treated.

General diagnostic pointers

• 1.

  Are history and symptoms helpful in determining etiology? Is there diplopia, childhood strabismus (if the patient is an adult), and is there DVD?

• 2.

  Is incomitance greater vertically or horizontally? If it is greater vertically, consider a restriction superiorly or inferiorly, or palsy of a vertical rectus. If the largest difference is horizontal, consider an oblique problem.

• 3.

  Is there a limitation of rotation? Differentiate restriction from paresis with forced duction and active force generation testing.

• 4.

  Is there substantial torsion? If so, consider oblique problems or a vertical restriction.

• 5.

  Might the patient be fixing with the involved eye? Always consider this if there is asymmetric best-corrected visual acuity. Check for a secondary deviation.