For more than 25 years, the King-Devick Test has been a proven indicator of oculomotor inefficiencies regarding eye movements during reading with hundreds of published papers in 19 different countries evaluating the test.
Published medical studies have determined that deficiencies in saccadic eye movements can be an indicator of mild Traumatic Brain Injury (mTBI) or concussions.  Recent studies published in Neurology and the Journal of The Neurological Sciences have determined that post head-trauma related deficiency in the King-Devick Test is an indicator of mild TBI or concussions.

As defined in Dorland's Medical Dictionary, 31st Edition and Mosby’s Medical Dictionary, 8th Edition:King-Devick Test /kingdev’ik/: a tool for evaluation of saccade, consisting of a series of charts of numbers. The charts become progressively more difficult to read in a flowing manner because of increasingly more difficult spacing between the numbers. Both errors in reading and speed of reading are included in deriving a score. Developed by Drs. King and Devick-1976.

The King-Devick Test is an objective, physical method of evaluating visual tracking and saccadic eye movements. King-Devick Test is based on the time to perform rapid number naming. It involves reading aloud a series of single digit numbers from left to right on three test cards. Participants are asked to read the numbers on each card from left to right as quickly as possible but without making any errors. The sum of the three test card time scores constitutes the summary score for the entire test.