The King–Devick (K–D) test of rapid eye movements: A bedside correlate of disability and quality of life in MS
Introduction
Visual dysfunction is a leading cause of disability in multiple sclerosis (MS). Objective measurement tools that correlate with quality of life (QOL) scores such as optical coherence tomography (OCT) and MRI are important, though are costly, time consuming and not readily accessible [1], [2]. Additionally there are many quality of life measurement tools in MS that are both reliable and valid, but are not performed because of the time required [3]. While there are clinical tools to assess afferent visual function, such as low-contrast letter acuity [1], those that can potentially capture efferent function involving intact eye movements have not been assessed. A visual screening tool that is rapid, easy to administer and does not require expensive equipment is a welcome addition for MS clinical trials.
The King–Devick (K–D) test was originally designed as a predictive tool of reading difficulties in children, and requires saccadic eye movements [4], [5]. The K–D test is based on the speed of rapid number naming, and requires intact eye movements, particularly saccades [6]. The K–D test has been shown by several recent studies to be a measure that effectively identifies concussed athletes post-injury on the sidelines. Time scores for the K–D test are significantly higher (worse) in athletes immediately following concussion, consistent with the involvement of widely distributed visual pathways [7], [8], [9], [10]. Such pathways are also affected in MS and, to date, a rapid performance measure that potentially captures efferent visual function in trials has not been identified.
The purpose of this investigation was to examine the potential role for the K–D test as a rapid visual performance measure in an MS cohort. We also sought to determine the relation of K–D time scores with afferent visual function (low- and high-contrast acuity), RNFL thickness by OCT, neurologic disability, and vision-specific QOL in MS patients.
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Study participants
A convenience sample of patients with MS and disease-free controls at the University of Pennsylvania participated in this cross-sectional study. Patients were part of an ongoing collaborative study of MS visual outcomes, and were not selected based on clinical features, extent of disease, or symptoms. The diagnosis of MS was confirmed by standard clinical and neuroimaging criteria [11] and patients with comorbid ocular conditions unrelated to MS were excluded in the study. MS duration and
Results
Table 1 presents demographic and clinical data for patients with MS in our cohort. Patients had an average disease duration of 11 years (0–46 years), and 41% of eyes had a history of acute optic neuritis (ON). While most patients had relapsing remitting MS (89%), secondary progressive and primary progressive MS were also represented. The gender distribution was similar between patients and controls (70% female for MS vs. 76% for controls; p = 0.39, t-test). Average age for patients and controls
Discussion
The K–D test, a < 2 minute bedside test of rapid number naming, captures visual dysfunction, neurologic impairment, and quality of life in patients with MS. K–D scores reflect work disability and neurologic impairment, as well as structural changes in the afferent visual pathway measured by OCT imaging. Findings of this study provide initial evidence in support of the K–D test as a rapid visual performance measure for MS trials.
A previous study examining the K–D test as a ringside measure in
Conflict of interest
Dr. S. Galetta has received speaking and consulting honoraria from Biogen-Idec, Questcor, and Teva. Dr. Balcer has received speaking and consulting honoraria from Biogen-Idec, Bayer, and Questcor. The authors have no financial interest in the King–Devick test; the work performed in this study was not funded by any of the above sources.
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