Use of the King–Devick test in youth and adolescents: A systematic review of diagnostic accuracy, validity and reliability
This systematic review of 55 studies involving over 16,000 youth and adolescents concludes that while the King–Devick test demonstrates excellent reliability, its diagnostic accuracy is limited by substantial heterogeneity and low-certainty evidence, positioning it best as an adjunctive tool within a multimodal concussion assessment framework rather than a standalone diagnostic instrument.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
When a young athlete takes a hard hit to the head, the brain's internal wiring can get scrambled, often without any visible bruise or loss of consciousness. This injury, known as a concussion, disrupts the delicate systems that control how we move our eyes, focus our attention, and process information quickly. Because the brain is still developing in children and teenagers, these systems behave differently than they do in adults, making it harder to spot the injury. Doctors and trainers need a way to check if the brain is working normally, and for years, they have looked for a simple, fast test that could be used on the sidelines of a game. One such tool, the King-Devick test, asks a person to read a series of numbers aloud as quickly as possible. The idea is that if the brain is injured, the eyes will struggle to jump from one number to the next, causing the person to take longer or make mistakes. It is a test of speed and accuracy, designed to catch the subtle signs of a concussion that a simple symptom checklist might miss.
A team of researchers recently set out to see if this test actually works as well as hoped when used on young people, from elementary school children up to teenagers. They gathered every available study that had used the King-Devick test on youth and adolescents, looking at both sports-related head injuries and other neurological conditions. Their goal was to determine if the test is reliable enough to be trusted and if it can accurately tell the difference between a healthy brain and one that has been injured. They analyzed data from 55 different studies involving more than 16,000 participants. The researchers looked at how consistent the test results were when the same person took it multiple times, and they checked how often the test correctly identified a concussion versus how often it missed one or gave a false alarm.
The findings revealed a complex picture. On the one hand, the test appears to be quite consistent when a person takes it under the same conditions; if a young person reads the numbers quickly today, they are likely to do so again tomorrow, provided they have not been injured. However, the researchers found that the results varied wildly depending on who was being tested, where the test was given, and how the data was analyzed. When they tried to combine all the results to get a single answer about how good the test is at diagnosing a concussion, the numbers did not line up neatly. The ability of the test to correctly identify a concussion was moderate, meaning it caught many but not all cases, while its ability to correctly identify someone who did not have a concussion was good. Yet, because the studies were so different from one another, the researchers could not be certain that these numbers would hold true in every situation.
One of the most significant discoveries was that there is no single, agreed-upon rule for what counts as a "failed" test. Some studies said that if a person took even two seconds longer than their usual time, it was a sign of injury. Others said the difference needed to be five seconds, while some researchers argued that any increase in time or any mistake was enough to flag a problem. This lack of a standard cutoff makes it difficult for a coach or a parent to know exactly what to look for. Furthermore, the researchers noted that young people often get better at the test simply by practicing it. A child might take longer to read the numbers the first time they try, and faster the second time, not because their brain is healing, but because they have learned the pattern. This "learning effect" can hide the signs of an injury if the test is not managed carefully.
The quality of the studies themselves also raised concerns. The researchers found that most of the studies they reviewed had flaws in how they were designed or how they reported their results. Many did not use a clear standard to confirm who actually had a concussion, and some compared injured athletes to healthy people from completely different groups, which can skew the results. Because of these issues, the researchers concluded that the evidence supporting the test is not strong enough to stand on its own. They determined that the test should not be used as the only tool to decide if a young person has a concussion. Instead, it works best as part of a larger check-up that includes looking at symptoms, checking balance, and testing other brain functions.
Ultimately, the King-Devick test remains a promising tool for spotting potential brain injuries in young athletes, but it is not a magic bullet. It is a helpful piece of a much larger puzzle. The researchers suggest that for the test to be truly useful, medical professionals need to compare a young person's current performance to their own personal baseline, measured before any injury occurred, rather than relying on a fixed time limit that applies to everyone. They also recommend that the test be given frequently, perhaps every six months, to account for the rapid changes in the developing brain. Until more high-quality studies are done to settle the questions of how to interpret the results and what the cutoffs should be, the test should be viewed as a supportive screen that helps guide a decision, rather than a final verdict on a young athlete's health.
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