The manner in which the eyes scan during a reading-related task may be an indicator of Alzheimer's disease. This was demonstrated in a recent study in the Alzheimer's Disease and Associated Disorders Journal using a test called the King-Devick.

The King-Devick Test was initially developed as tool to help determine reading problems in children related to how the eyes scanned the page. It was a flip book with a series of reading cards that tested horizontal saccadic eye movement that was comparable to a reading pattern.

The test later was recognized as having application for diffuse brain injury, such as concussion, and is available in a tablet application. It has been used widely in sports to help determine a pull from play. More recently, a study found the test beneficial to determine function and ability to return to work or battlefield when there is a mild traumatic brain injury in military fighters.

The group studying the test in Alzheimer's disease evaluated 135 healthy adults, 39 with mild cognitive impairment and 32 with Alzheimer's disease. They found the test distinguished between the groups with pathology and the healthy adults. The time differences were small — 48 seconds for the controls and 52 for the groups with pathology — but significant.

The King-Devick Test has also been found to be helpful in assessing function in other neurological diseases such as Parkinson's disease and hypoxia.

It is not surprising that tests of visual function can be useful in many different types of neurological problems. The nerves associated with the light-sensitive cells of the eye comprise 30 percent of the cortex, compared to 8 percent of the cortex associated with touch and 3 percent for hearing.

When vision is coordinated with eye movement and other parts of the brain, it takes up over 60 percent of the brain. This is why vision and the coordination of eye movement are vulnerable to disease and injury.

Eye movement dysfunctions have long been recognized as one of the visual disturbances in Alzheimer's disease. A review of the literature related to Alzheimer's disease and eye movement published this spring concluded that the diagnosis of eye movement dysfunction does not show any superiority over other tests of neuropsychological function to differentiate Alzheimer's disease from other cognitive diseases.

However, after ruling out other causes such as age-related cataracts, retinal disease and uncorrected distance or near refractive errors, a test such as King-Devick certainly can be useful in demonstrating factors associated with early dementia, such as poor reading function.

A better understanding of the functional deficits related to Alzheimer's disease allows for better comprehensive care.