Dissociated vertical deviation (DVD) is an innervational disorder found in more than 50% of patients with infantile strabismus (esotropia or exotropia). There are 2 explanations for the origin of DVD. One theory is that DVD is a vertical vergence movement to damp latent nystagmus, with the oblique muscles playing the principal role. An alternative theory suggests that deficient fusion allows the primitive dorsal light reflex, which is prominent in other species, to emerge.
Dissociated vertical deviation usually presents by age 2 years, whether or not any horizontal deviation has been surgically corrected. Either eye slowly drifts upward and outward, with simultaneous extorsion, when occluded or during periods of visual inattention (Fig 11-8). Some patients attempt to compensate by tilting the head, for reasons that still have not been conclusively identified.
DVD is usually the most prominent component of the dissociated strabismus complex (DSC), but sometimes the principal dissociated movement is one of abduction (dissociated horizontal deviation, DHD), and occasionally it is almost entirely a torsional movement (dissociated torsional deviation, DTD). DVD is usually bilateral but is frequently asymmetric. It may occur spontaneously (manifest DVD) or only when 1 eye is occluded (latent DVD). An eye with latent DVD can give the appearance of inferior oblique overaction when it is occluded by the nose during adduction. In addition to DHD, latent nystagmus and horizontal strabismus are often associated with DVD. These entities are manifestations of deficient binocular vision.
Measurement of DVD is difficult and imprecise. In one method, a base-down prism is placed in front of the upwardly deviating eye while it is behind an occluder. The occluder is then switched to the fixating lower eye. The prism power is adjusted until the deviating eye shows no downward movement to refixate. These steps are then repeated for the other eye. Measurements obtained with this technique are confounded by any coexisting true hypertropia, but it does provide a rough estimate for surgical planning.
Figure 11-8 Dissociated vertical deviation, left eye. A, Straight eyes during binocular viewing conditions. B, Large left hyperdeviation immediately after the eye is covered and then uncovered. C, The left eye comes back down to primary position without a corresponding right hypotropia.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.