A vertical deviation can be termed a hyperdeviation of the higher eye or a hypodeviation of the lower, fellow eye. By convention, vertical deviations are named according to the hypertropic eye. However, the term hypotropia of the nonfixating eye is used to describe the patient who has a strong fixation preference for the hypertropic eye.
Surgical treatment of these conditions is discussed in Chapter 14.
A Clinical Approach to Vertical Deviations
The evaluation and diagnosis of vertical deviations are complicated by the need to consider dissociated vertical deviation (DVD). In a patient with a completely comitant deviation, there is no movement of either eye on prism alternate cover testing with the same amount of prism used for either eye (prism placed base down over one eye or base up over the other). When there is an incomitant hyperdeviation due to restriction or cyclovertical muscle paresis, the amount of prism needed to neutralize the deviation may be different depending on which eye is fixating. This is the difference between a primary and secondary deviation according to Hering’s law (see Chapter 4). Once the neutralizing prism for a given eye is found, however, neither eye moves when alternate cover testing is performed.
In some cases, the examiner encounters a more confusing situation that appears to violate Hering’s law. For example, suppose the examiner finds the prism that neutralizes a patient’s right hypertropia. That is, if the prism is held over an occluded right eye with the left eye fixating, there is no movement of the right eye when the occluder is moved to the left eye, and fixation switches to the right eye. However, when the occluder is moved back to the right eye, the left eye moves (either upward from a hypotropic position under cover or downward from a hypertropic position) as it resumes fixation. This inability to find a single prism that neutralizes the refixation movement for both eyes indicates the presence of DVD.
Some patients have both “true” hypertropia and DVD. In these patients, there is no way to quantify how much of the deviation is DVD and how much is true hypertropia, although several estimation methods have been advocated. Often, however, one is predominant and the other, smaller component can be ignored. For the sake of simplicity, this chapter does not discuss true hypertropia and DVD in combination but only as separate entities.
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.