Vertical & Dissociated Deviations

Hypertropia Terminology

Hypertropia is a manifest upward deviation of one eye relative to the other. It belongs with hypotropia (downward), esotropia (inward), and exotropia (outward) as the four directions a manifest tropia can take. Like the horizontal tropias, a hypertropia can be comitant or incomitant depending on whether the vertical offset changes with gaze direction. An incomitant hypertropia is the classic presentation of an isolated cyclovertical muscle palsy, worked up with three-step testing.

Dissociated Vertical Deviation (DVD)

Dissociated vertical deviation is defined by its behavior, not by a fixed direction relative to the fellow eye. Whichever eye is occluded, or simply receiving reduced binocular stimulation, drifts slowly upward; when the cover is removed, that eye drifts back down to reestablish fixation. Either eye can show the drift, and which eye drifts alternates. What separates DVD from an ordinary vertical tropia is that it does not obey Hering's law, the principle that yoke muscle pairs receive equal, linked innervation. In DVD, the two eyes' drifts are dissociated from each other rather than linked as a conventional yoke pair would be. That dissociation is the source of the name.

DVD is frequently bilateral and asymmetric, and it keeps close clinical company. It is most often seen alongside infantile esotropia and latent or manifest latent nystagmus. DVD, infantile esotropia, latent nystagmus, and inferior oblique overaction are often grouped together as the infantile strabismus syndrome complex. The leading explanation is a shared cause: disruption of normal binocular fusion development very early in infancy. Infantile esotropia begins, by definition, before normal binocular vision has had a chance to establish itself, so it interferes with the developmental wiring that would otherwise produce stable, Hering's-law-obedient yoke muscle control. DVD, on this model, is a residual signature of that early disruption rather than an unrelated muscle problem.

Surgery is reserved for drifts large enough to draw attention or interfere with binocular function. Superior rectus recession is the most commonly used procedure, sized to the magnitude of the drift and performed bilaterally when both eyes are affected. Anterior transposition of the inferior oblique is preferred instead when inferior oblique overaction coexists with DVD, since it addresses both findings in one procedure. Most series report only a 60 to 80 percent reduction in the deviation; some residual or recurrent drift is expected, not a sign the surgery failed.

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