The King-Devick Test (K-D Test) is defined by Mosby’s Medical Dictionary as a tool for evaluation of saccade, consisting of a series of test cards of numbers. The test cards become progressively more difficult to read due to variability of spacing between the numbers. Both errors in reading and speed of reading are included in deriving a score. Saccades are quick, simultaneous movements of both eyes.
The King-Devick Test was developed in 1976 by Alan King, O.D. and Steven Devick, O.D. as an indicator of saccadic performance as it relates to reading ability. In 1983, a sample of 1202 children ages six to fourteen was screened using the K-D Test. The study done by the State University of New York (SUNY) concluded that the test was quick and easy to score and could be administered by non eye care practitioners. For more than 25 years, the King-Devick Test has been a proven indicator of oculomotor inefficiencies regarding eye movements during reading. The King-Devick Test (K-D Test) is utilized as a tool in schools, eye care and psychologist offices to help detect learning disabilities, including dyslexia.
The King-Devick Test (K-D Test) is an objective, physical test based on the measurement of the speed of Rapid Number Naming (reading aloud single digit numbers from three test cards), and captures impairment of eye movements, attention, language, and other correlates of suboptimal brain function. The sum of the three test card time scores constitutes the summary score for the entire test. The test can be administered in less than two minutes. In 2011, researchers published findings supporting the utility of the King-Devick Test as a sideline remove-from-play concussion screening tool.
The King-Devick Test, a remove-from-play concussion screening, is a two-minute test that requires an athlete to read single digit numbers displayed on test cards, a computer, or an iPad and can be administered by coaches, athletic trainers, medical professionals and parents. Athletes must create a preseason or pregame baseline. A baseline is the cumulative amount of time it takes to read the three test cards aloud. For baseline testing, the entire test should be administered twice. The fastest cumulative time of the two attempts with no errors is considered to be the baseline. Immediately or soon after a suspected head trauma, the athlete is given the King-Devick Test once and if the time needed to complete the test is any longer than the athlete’s baseline test time and/or if there are errors, the athlete should be removed-from-play and should be evaluated by a licensed professional. The test has relevance to sports such as: football, hockey, soccer, basketball, lacrosse, rugby, and all other contact or collision activities. The King-Devick Test (K-D Test) is used in many high school and college athletic programs. The test is also used at the professional level in the National Hockey League (NHL), Major League Soccer (MLS), Major League Lacrosse and professional arena football.
In 2010, researchers from the University of Pennsylvania Perelman School of Medicine investigated the King-Devick Test as a potential rapid sideline screening test for concussion in a cohort of 39 boxers and mixed martial arts (MMA) fighters. The K-D Test was administered pre-fight and post-fight. Post-fight K-D time scores were significantly higher (worse) for participants who had sustained head trauma during the match compared to their pre-fight scores. Additionally, statistical analysis showed that the K-D test had high test-retest reliability. The researchers concluded that the King-Devick Test is an accurate and reliable method for identifying athletes with head trauma, and is a strong candidate rapid sideline screening test for concussion.
In 2010, a longitudinal study was conducted involving 219 athletes from the University of Pennsylvania varsity football, sprint football, women’s and men’s soccer and basketball teams. Each subject underwent baseline King-Devick (K-D testing) prior to the start of the 2010-11 playing season. For athletes who had concussions during the season, K-D testing was administered immediately on the sidelines and changes in score from their baseline were determined. For the 10 athletes who had concussions, K-D testing showed worsening from their baseline score/time. Additionally, the effect of the physical exertion on K-D test performance was studied in a subgroup analysis of men's basketball-players who received K-D testing immediately following an intense two hour scrimmage. These athletes, none of which sustained concussion, did not show any worsening of their K-D score, but instead showed improvement from baseline even in the setting of post-workout fatigue revealing that the K-D test is robust to fatigue. This study of collegiate athletes provided further evidence in support of the K-D Test as a strong candidate rapid sideline visual screening tool for concussion.
In August 2011, Ralph Nader publicly called for the mandatory implementation of the King-Devick Concussion test in high school and youth sports. “Too many sports organizations, from little leagues to the professional level, continue to have their heads in the sand when it comes to concussion safety and prevention measures," said Nader. “The growing mound of research showing the often devastating long-term effects of sports-related brain trauma demands that we take proactive measures to protect our young athletes’ brains. The King-Devick test is a simple and objective sideline screening test that can be administered by coaches, trainers and parents.” Some sports medicine doctors and trainers have called the King-Devick test the “missing link” for practical sideline management of concussions due to its simplicity, objectivity and effectiveness.
In 2012, the K-D test was studied in the setting of amateur rugby athletes over the course of one competitive season in New Zealand. In this pilot study of 50 rugby athletes (mean age 19.3 years ± 4.0 standard deviation), the K-D test was able to accurately identify three players with witnessed head trauma who were subsequently diagnosed with concussion. By testing all athletes post-match, the K-D test was able to identify two players that had sustained a concussive injury that was neither reported nor witnessed. This pilot study revealed that the K-D test detected un-witnessed concussions by simply testing all players after contact play.
In 2012, the K-D test was included in a comprehensive review comparing sports-concussion testing tools. The review proposed that the K-D test has the potential to capture brain impairment not observed in standard neurocognitive testing. It reported that the K-D test is administrable in the quickest amount of time (less than 2 minutes as compared to others requiring upwards of 20 minutes for test administration). The K-D test does not require a medical professional to administer, assesses more the 50% of the brain’s pathways and gives a definite, and gives an objective outcome measure making it practical for sideline use at all levels of sports.
Before the fall football season of 2012, 80 King-Devick test kits were donated to the Chicago Public Schools (CPS) high school football programs by the Dave Duerson Foundation to ensure that every CPS football team had an effective sideline remove-from-play concussion screening tool. The donation was made in an effort to contribute to a safer game of football in the memory of Dave Duerson who was a former Chicago Bears football player.
In 2013, the K-D test was investigated in a prospective observational cohort study of 37 (mean age 22.0 years ± 4.0 years) amateur New Zealand rugby union players across 24 games. There were 22 concussive incidents recorded over the duration of the competitive season. Five concussive incidents were witnessed and accurately identified by the K-D test. Routine post-match screening for concussion with the K-D test identified an additional 17 unrecognized incidents in which players had not shown, or reported, any signs of symptoms of a concussion but who had sustained meaningful head injury. This study supported previous studies that the K-D test is sensitive to neurological changes such as those seen with sports-related concussion. 
In 2013, a prospective study evaluated the K-D test in the Philadelphia Flyers professional ice hockey team. In this exploratory analysis of 27 athletes (mean age 28.0 years ± 5.0 years) two players tested rinkside immediately following concussion demonstrated worsened K-D test scores from baseline. For SCAT2 SAC components, however, these athletes showed no differences between baseline and rinkside concussion testing, but reported symptoms of concussion. Additionally, at baseline testing for the cohort, lower scores for the SCAT2 Standardized Assessment of Concussion (SAC) Immediate Memory Score and overall SAC score were associated with greater (worse) times required to complete the K-D test. Both working and saccadic eye movements share closely related anatomical brain structures, including the dorsolateral prefrontal cortex (DLPFC) an area vulnerable to injury in concussion and therefore may explain some of the eye movement and memory related symptoms in athletes and other patients with concussion. 
In 2013, a study of the K-D test in a cohort of 47 high school football players during the 2012 football season was presented at the prestigious Association for Research in Vision and Ophthalmology (ARVO) annual meeting. During the season, three athletes sustained concussion and demonstrated diminished KD test performance times when tested shortly after the on-field injury. K-D test times were diminished by 41%, 100% and 143% respectively in these three athletes. Test-retest reliability was analyzed using intraclass correlation coefficients (ICC) between baseline and end of season data and demonstrated high test-retest reliability, supporting previous studies. This study showed that the K-D test is effective as a rapid sideline tool to identify concussion at the high school youth sports level. 
In 2013, a study comparing the Symbol Digit Modalities Test (SDMT) and the K-D test in a cohort of 16 mixed martial arts fighters was presented at the European Neurological Society Annual Meeting. Fighters were given both tests pre and post-fight by a single examiner. Changes in scores were compared for those with head trauma during the fight vs. those without. There was a modest correlation between head trauma during the match and worsening (increase) in K-D scores (r=0.54, p=0.015), the actual change (r=0.42, p=0.055) and the percentage change in K-D scores from pre to post-fight (r=0.50, p=0.025). Only 1 fighter without head trauma had a worsening of K-D score by ≥5 seconds. There was only small to medium correlation between worsening of SDMT score (decrease) and K-D score. There was no correlation between SDMT scores and concussions during the match. This study confirms that the K-D test, but not the SDMT, is reliable in rapidly identifying athletes with head trauma. 
The King-Devick saccadic eye movement test is a clinical screening tool for eye movement dysfunctions. The test is easy to administer and has been incorporated in many visual screening protocol used by non-professionals. The test is also used in formal investigation into understanding learning related visual problems. Children attending New York Public schools were screened using the King-Devick Test (K-D Test) and there was a significant correlation with their citywide achievement test scores and was significant for predicting those students in the lower 25% of the class for all grades.
The more educators can be educated in accurate detection of vision problems; more can be done in helping children achieve academically as well. Saccadic eye movement deficiencies can be improved with training and correspondingly reading performance can be improved. Performance on the King-Devick Test is related to reading performance as young as 5 and 6 year olds in kindergarten. In addition, the King-Devick Test has shown to be statistically and practically significant in the reading development in adults.
The King-Devick Test is a readily available and useful tool for assessing residual oculomotor functions, and its components can also be used for in-school eye-movement training purposes. The King-Devick Test comprises one demonstration card and three test cards, which contain several rows of random numbers that become progressively more difficult to follow with either spotting or tracking skills. The test is scored based on age, speed and accuracy. Participants are asked to read the numbers on the three test cards from left to right as quickly as possible without making any errors. The sum of the three test card times, along with number of errors reading the test cards are recorded. The score is compared to pass/fail normative data for subjects from 6 years old through adulthood.
In addition to detecting learning disabilities, the King-Devick Test (K-D Test) has been studied as an in-school remediation tool to improve reading fluency. Students in grades 2-4 were screened for reading inefficiency using the King-Devick Test (K-D Test). Subjects who failed the test were entered into the study. A verbalized reading evaluation was administered to all subjects to serve as a measure of baseline and post-treatment reading performance. The treatment consisted of Rapid Number Naming therapy using proprietary King-Devick Test LLC software. The results of the study showed a statistically significant improvement in reading fluency among individuals who underwent Rapid Number Naming therapy in school for three 20 minute sessions (one hour total) per week for just six weeks.
Severe Sleep Deprivation Functionality Prediction
In April 2012, a study was published investigating the effect of severe sleep deprivation on the speed and accuracy of eye movements as measured by the King-Devick (K-D) test. Neurology residents and staff from the University of Pennsylvania Health System underwent baseline K-D testing followed by post call K-D testing. The conclusion of the study supported that the K-D test is sensitive to the effects of severe sleep deprivation on cognitive functioning, including rapid eye movements, concentration, and language function. Severe fatigue appears to reduce the degree of improvement typically observed in K-D test.
Multiple Sclerosis Quality of Life Measure
The King-Devick (K-D) Test of Rapid Eye Movements: A Bedside Correlate of Disability and Quality of Life in Multiple Sclerosis was a distinguished poster during poster presentations at the 38th Annual North American Neuro-Ophthalmology Society Meeting linking the King-Devick Test to multiple sclerosis.
In 2012, the King-Devick test was studied in a cohort of patients with Multiple Sclerosis (MS) (n=40) and disease-free controls (n=20) at the University of Pennsylvania. K-D scores in the MS group were significantly higher (worse) compared to the disease-free control group. This study revealed that the K-D test, a less than one minute bedside assessment of rapid number naming, correlates well with binocular visual function, disability and vision specific quality of life in MS. 
In 2013, the K-D test was studied in a larger MS cohort (n=81) and compared to disease free controls at New York University. In the MS cohort, K-D scores were significantly worse compared to controls. The K-D scores reflected work disability as well as structural changes as measured by retinal Optical Coherence Tomography (OCT). Additionally, abnormal binocular visual acuity and a history of optic neuritis, both common ocular complications of MS, were associated with worse K-D Scores suggesting that the K-D test captures both afferent and efferent components of vision. 
Parkinson's disease Functionality Measure
In 2013, the King-Devick test was first studied in a Parkinson's disease (PD) cohort at the Arizona Parkinson's Disease Consortium and the Mayo Clinic. PD patients were compared to Essential Tremor (ET) patients and disease-free controls. K-D scores were significantly higher (worse) for the PD group as compared to the ET group and the control group even after adjusting for age and sex. This was the first study of the K-D test in Parkinson's disease and showed that the K-D test may be a quick tool for quantifying visual and cognitive function in Parkinson's disease at bedside.  
In 2013, the King-Devick test was studied as a tool for the detection of hypoxia in a Mayo Clinic study. There were 25 subjects enrolled in the study. Cognitive performance was assessed by using the King-Devick Test. The performance of the subjects on the K-D test was measured in normoxia followed by hypoxia (8% O2 equivalent to 7101 m) and then again in normoxia. K-D test completion time in hypoxia for 3 min was significantly longer than the Baseline Test (54.5 ± 12.4 s hypoxic vs. 46.3 ± 10.4 s baseline). Upon returning to normoxia the completion time was significantly shorter than in hypoxia (47.6 ± 10.6 s post-test vs. 54.5 ± 12.4 s hypoxic). There was no statistically significant difference between baseline test and post-test times, indicating that all subjects returned to their normoxic baseline levels. SpO2 decreased from 98 ± 0.9% to 80 ± 7.8% after 3 min on hypoxic gas. During the hypoxic K-D test, SpO2 decreased further to 75.8 ± 8.3%. In this study the K-D test has been shown to be an effective neurocognitive test to detect hypoxic impairment at early pre-symptomatic stages. The K-D test may also be used to afford a reassessment of traditional measures used to determine hypoxic reserve time.   
In October 2013, a Mayo Clinic press release quoted Jan Stepanek, M.D., the Aerospace Medicine Program Director and Co-Director of the Aerospace Medicine & Vestibular Research Laboratory. "This study provides an objective indication of hypoxia that is involuntary, reliable and repeatable," Dr. Stepanek said. "This means that people can be tested for cognitive declines before having symptoms, because often people won't have symptoms until it is too late." 
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