Interventions for dissociated vertical deviation
Abstract
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
To assess the effects of surgical and non‐surgical interventions for dissociated vertical deviation (DVD).
Background
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.
Objectives
To assess the effects of surgical and non‐surgical interventions for dissociated vertical deviation (DVD).
Methods
Criteria for considering studies for this review
Types of studies
We will include only randomized clinical trials (RCTs) in this review. However, as it is anticipated that there will be very few RCTs, the searches will be run without a filter to identify all reports of trials on this topic.
Types of participants
We will include people of any age with dissociated vertical deviation (DVD) undergoing any surgical or non‐surgical intervention.
Types of interventions
We will include any trial comparing surgical versus no intervention or non‐surgical intervention types, or one surgical intervention compared to another surgical intervention. A set of comparisons will include:
-
Any type of surgical intervention versus no intervention
-
Any type of surgical intervention versus non‐surgical intervention
-
Any type of surgical intervention versus another type of surgical intervention
-
Any type of non‐surgical intervention versus no intervention
-
Any type of non‐surgical intervention versus another type of non‐surgical intervention
Types of outcome measures
Primary outcomes
The primary outcome of the review will be the proportion of patients with success, defined as reduction of the hyperdeviation in each eye to 4 prism diopters (pd) or less, based on a prism under cover test and assessed at one year from intervention. The total deviation measured in this way is the sum of the DVD and any true hypertropia; it is not currently possible to separate these components (Tarczy‐Hornoch 2008). Assessment by prism and alternate cover may yield the same data as the prism under cover test, as long as care is taken to dissociate the patient; therefore prism and alternative cover test data will be used when prism under cover test data are not available. Wherever prism and alternate cover test are to be used they must be collected explicitly fixing right eye and then fixing left eye.
Secondary outcomes
All secondary outcomes will be assessed at one year after the intervention as data are available. Secondary outcomes of the review will include the following:
-
Total magnitude of hyperdeviation, measured with a prism under cover test (or prism and alternative cover test, when prism under cover test data are not available) of each eye separately, summed between both eyes. When prism and alternate cover test are to be used they must explicitly be collected fixing right eye and then fixing left eye.
-
Proportion of day (duration) of misalignment (as data are available).
-
Quality of life scores from vision‐specific quality of life instruments, such as the National Eye Institute (NEI) Visual Function Questionnaire‐25 (VFQ‐25) for adults, Adult Strabismus‐20 Questionnaire (AS‐20) for adults, and vision‐specific pediatric quality of life instruments for children.
-
Proportions of any adverse events that occurred during or after any surgical/non‐surgical interventions.
-
Magnitude of simultaneous prism and cover test of the deviating eye or, if deviating eye not noted, the eye with greatest DVD type deviation (at either distance or near fixation).
-
Magnitude of prism under cover test or prism and alternate cover test of the deviating eye or, if deviating eye not noted, the eye with greatest DVD type deviation (at either distance or near fixation).
Search methods for identification of studies
Electronic searches
We will search the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library), Ovid MEDLINE, Ovid MEDLINE In‐Process and Other Non‐Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE, EMBASE, PubMed, Latin American and Caribbean Health Sciences Literature Database (LILACS), the metaRegister of Controlled Trials (mRCT) (www.controlled‐trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We will not use any date or language restrictions in the electronic searches for trials.
See: Appendices for details of search strategies for CENTRAL (Appendix 1), MEDLINE (Appendix 2), EMBASE (Appendix 3), PubMed (Appendix 4), LILACS (Appendix 5), mRCT (Appendix 6), ClinicalTrials.gov (Appendix 7) and the ICTRP (Appendix 8).
Searching other resources
We will search the reference lists of relevant studies to identify any further reports of trials that might be eligible for inclusion in the review.
Data collection and analysis
Selection of studies
Two authors independently will screen the titles and abstracts identified from the electronic searches and classify them as 'definitely include', 'unsure', or 'definitely exclude'. We will retrieve full text articles for those classified as 'definitely include' or 'unsure', and re‐assess the eligibility based on the inclusion criteria of the review. For any disagreements between the two authors, we will consult the third author to reach final agreement, and will record the study characteristics and assess the risk of bias for each included study. For studies excluded during full text screening, we will record the reason for exclusion in the 'Characteristics of excluded studies' table. We will contact the study investigators for missing information.
Data extraction and management
Two authors independently will extract data for primary and secondary outcomes using a data collection form developed in collaboration with the Cochrane Eyes and Vision Group. After reaching consensus regarding extracted data, one author will enter the data into RevMan 5.2 (RevMan 2012), and a second author will verify the entered data.
Assessment of risk of bias in included studies
Two authors independently will assess the risk of bias of each included study using the methods described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011), as part of the data extraction process. We will assess the following domains: sequence generation, allocation concealment, masking (blinding) of participants, personnel and outcome assessors, incomplete outcome data, selective outcome reporting, and any other sources of bias. To resolve any disagreements in bias assessment, we will consult the third review author. For missing or unclear information, we will contact investigators to obtain further information. Whenever the investigators contacted do not respond within two weeks, we will assess the available information. Each domain will be labeled as high risk of bias, low risk of bias, or unclear risk of bias. The assessments will be recorded in the 'Risk of Bias' table.
Measures of treatment effect
The primary outcome for this review will be a dichotomous outcome. We will report the measure of effect as a relative risk (risk ratio) with a 95% confidence interval. We will report the dichotomous secondary outcome (proportions of adverse events) in the same manner. For continuous outcomes (all other secondary outcomes), we will estimate the mean values and 95% confidence intervals. We also will calculate standardized mean differences (SMDs) when continuous outcomes are measured using different scales.
Unit of analysis issues
For surgical success, total magnitude of hyperdeviation, and proportion of day of misalignment, and quality of life scores, the unit of analysis will be the patient, because interventions for DVD may appear to improve the DVD in one eye but make the DVD worse in the opposite eye. If the hyperdeviation is not summed for both eyes (i.e. if data are analyzed by patient instead of eye), then an intervention that improves the hyperdeviation in one eye but makes the hyperdeviation worse in the fellow eye erroneously would be considered successful. We will refer to Chapter 9.3 of the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2011) for unit of analysis issues.
Dealing with missing data
We will contact study investigators for any missing or incomplete data. If the investigators do not respond within two weeks, we will use the data available.
Assessment of heterogeneity
We will use the I2 statistic (%) to determine the proportion of variation due to heterogeneity, with a value above 50% suggesting substantial statistical heterogeneity. We will assess clinical and methodological heterogeneity by examining potential variations in participant characteristics, inclusion/exclusion criteria and assessments of primary and secondary outcomes.
Assessment of reporting biases
If we include 10 or more studies, we will use funnel plots to identify any publication reporting biases.
Data synthesis
We will determine whether data synthesis is appropriate depending on the measure of heterogeneity calculated. If the I2 statistic suggests substantial statistical heterogeneity (> 50%), we will not synthesize the data; instead, we will present results in a narrative summary. If the I2 statistic is less than 50% (not indicating substantial heterogeneity), we will combine study results using random‐effects meta‐analysis. If there is no heterogeneity detected, or greater than three studies are included for an outcome, we will use a fixed‐effect model.
Sensitivity analysis
We will conduct sensitivity analyses to determine the impact of excluding studies assessed as being of lower methodological quality, industry‐funded studies, and unpublished studies.
