Description of the condition
Dissociated vertical deviation (DVD) is defined as an upward drifting of one eye when the other eye is fixing on a target (Brodsky 1999). The deviation often involves both eyes but is most frequently asymmetric, such that the primary concern is vertical drifting of one eye (Helveston 1980). The deviation may be manifest (spontaneously visible to others) or latent (only seen when the eye is covered), and it is the manifest form that leads parents and patients to seek treatment. Patients only very rarely complain of double vision, because the misalignment is associated with central suppression of the image from the deviated eye (the image is not perceived), and parents and patients seek treatment for psychosocial reasons or for subjective strain.
DVD was first described in 1895 by Stevens who called it "anaphoria" or "anatropia" (Wolff 1978). DVD has also been referred to as "alternating hyperphoria", "double hyperphoria", "occlusion hyperphoria", "occlusion hypertropia", "alternating sursumduction", "double dissociated hyperphoria", "dissociated hyperphoria", "dissociated hypertropia" and "dissociated vertical divergence" (Wolff 1978).
DVD most often occurs in the context of pre-existent infantile strabismus, typically infantile esotropia and typically following surgery for esotropia (Arslan 2010). It may occur in up to 90% of cases of infantile esotropia (Helveston 1980; Neely 2001), but also may occur in the context of presumed infantile microstrabismus (Choi 2001) and exotropia (Lim 2008). DVD may also occur associated with acquired loss of vision in childhood (Kutluk 1995). The common feature of all these scenarios associated with DVD is "intense disturbance of binocular vision" early in childhood (Houtman 1991).
Not only does DVD present as a visually noticeable vertical ocular misalignment, but it may also result in a noticeable head tilt (Bechtel 1996; Brodsky 2004; Santiago 1998). There is controversy regarding whether DVD can cause symptoms of strain and whether intervention can improve those symptoms.
Although some authors suggest that DVD spontaneously resolves by adulthood (Fleming 1980), other authors report persistence of the condition (Sprague 1980) and report no spontaneous improvement (Harcourt 1980), such that many parents seek treatment for their children with DVD and many adults with DVD also seek treatment.
Some authors have commented that for the patient with asymmetric DVD, surgery on only one eye commonly leads to a need for surgery on the other eye, leading to the suggestion that asymmetric DVD should be addressed bilaterally (Noel 1982; Sargent 1976).
DVD is one of the least understood types of strabismus. Some investigators believe it is due to a vestigial righting reflex (Brodsky 1999; Brodsky 2002; Brodsky 2011), whereas others feel it is a nystagmus blocking mechanism (Guyton 1998; Guyton 2000; Guyton 2004). Other authors suggest that DVD results from unbalanced cortical input to subcortical pathways (ten Tusscher 2010). Despite lack of clarity regarding the pathophysiology of DVD, many patients undergo empirical treatment.
Description of the intervention
Patients with DVD are managed with either observation, optical blur to change fixation (Yue 2003), injection of Botulinum Toxin into the superior rectus (McNeer 1989) or surgery. Reported surgical techniques used for DVD are as follows: 1) weakening of the inferior oblique (Pratt-Johnson 1976; Strominger 2009), 2) anteriorization of the inferior oblique muscle (Bacal 1992; Black 1997; Bothun 2004; Burke 1993; Elliott 1981; Engman 2001; Fard 2010; Guemes 1998; Milot 1994; Mims 1999; Stager 1992; Nabie 2007; Nelson 2007; Quinn 2000), 3) anteriorization of the inferior oblique combined with resection (Farvardin 2002; Quinn 2000; Snir 1999; Wong 2003), 4) recession of the superior rectus muscle (Braverman 1977; Broniarczyk-Loba 2007; Magoon 1982; McCall 1991; Repka 1988; Schwartz 1991; Scott 1982; Varn 1997; Yu 1992), 5) recession of the superior rectus muscle with a posterior fixation suture (Esswein 1992; Kii 1994; Lorenz 1992; Sprague 1980), 6) superior rectus posterior fixation suture alone (Lorenz 1992), 7) resection of the inferior rectus (Esswein 1994; Noel 1982; Sargent 1976; Sargent 1979), 8) tucking of the inferior rectus (Arroyo-Yllanes 2007), 9) 4-muscle oblique surgery (Gamio 2002), and 10) superior oblique resection (Richard 1987). It is noteworthy that a wide spectrum of surgical approaches have been described for DVD.
DVD may be combined with other types of strabismus, for example esotropia and exotropia. This review will include studies of patients who also had such horizontal strabismus, but will not include people for whom intervention was designed to address pattern strabismus such as coexistent superior oblique overaction (McCall 1991), since it would not be possible to separate the components of the effects.
How the intervention might work
Non-surgical interventions, such as optical blur of the eye with the less pronounced DVD, may work by promoting fixation of the eye with the more pronounced DVD, and therefore make the DVD less noticeable. Strabismus surgery may reduce the tendency for the eye to drift upwards, either by mechanically restricting elevation or by reducing the upward force on the eye.
Why it is important to do this review
Although many patients undergo surgical or non-surgical treatment for DVD, whether or not to perform treatment and which type of treatment to perform appear to be more personal preference than evidence-based (Caputo 1999; Coats 2011). Therefore a comprehensive review is needed to evaluate whether any intervention is effective for DVD and which type of intervention is most effective.