Another alternative is the use of tests using a visual–verbal format. These tests are inexpensive, easily administered, and provide a quantitative evaluation of eye movements in a simulated reading environment (75). They assess oculomotor function on the basis of the speed with which a series of numbers can be seen, recognized, and verbalized with accuracy. Richman et al. (75) have raised questions about the validity of such assessment techniques because they do not account for automaticity of number naming. They devised a new test called the developmental eye movement (DEM) test that does account for this variable (76).

A second method is the use of timed and standardized tests. Several are available, including the Pierce saccade, King-Devick, and DEM tests. All three of these tests are designed on the same principle. The patient is asked to call off a series of numbers as quickly as possible without using a finger or pointer as a guide. The response times and number of errors are then compared to tables of expected values.

A potential problem with these tests is that young children may call off the numbers slowly, simply because they have difficulty with naming numbers. Both the Pierce and King-Devick tests fail to differentiate between a saccadic problem and difficulty with naming numbers (automaticity of letter naming). The DEM test is the procedure of choice because it does consider this issue (Fig. 1.8).

Another problem associated with the use of tests using the visual–verbal format is reliability. This question is important because the DEM is commonly used to evaluate progress during vision therapy. Of particular concern is the issue of variation and improvement due to learning effects. Oride et al. (77) have shown a significant learning effect with the Pierce saccade and King-Devick tests. Although Garzia et al. (76) reported that the DEM is a reliable and repeatable test, Rouse et al. (78) have reported conflicting results. Rouse et al. examined 30 third-grade students using the DEM and retested them 2 weeks later. They found a very low correlation for the DEM ratio score, which is an important finding for diagnosis. Orlansky et al. evaluated the repeatability of the DEM test with three consecutive administrations on two separate visits to 181 children between the ages of 6 years and 11 years 11 months. The within-session repeatability for vertical- and horizontal-adjusted time were good to excellent but were poor to good for ratio, and poor to fair for errors. The between-session intraclass correlation coefficients were fair to good for both the vertical and horizontal scores but poor for the ratio and error scores. The repeatability of the pass-fail diagnostic classification within a single session for each subject on test and retest was also compared. The percentage of patients who remained in the same classification ranged from 71% to 100% for both vertical and horizontal scores. Wider variability was seen with the ratio and error scores showing between 47% and 100% of the children remaining classified as pass or fail with repeated administrations of the DEM. Such findings suggest that ­children in this age range may show improvements in all four test scores without any intervention. The authors concluded that clinicians should be cautious about using the DEM test in isolation for reaching a diagnosis or monitoring the effectiveness of treatment for saccadic dysfunction. More recently, Tassinari and DeLand (79) investigated the DEM test-retest reliability in patients undergoing vision therapy. They reported good to excellent intrasubject test-retest reliability. This study is important because it is the first study to evaluate the

reliability of the DEM with vision therapy patients. It is apparent that there are issues with the repeatability of the ratio and error scores for the DEM. The horizontal-adjusted time has the best repeatability and seems to be the most appropriate way to follow progress during therapy. As a clinical guideline, Orlansky et al. (80) found that when monitoring for treatment effect, differences in the horizontal-adjusted time must show more than 64 s of change for 6-year-olds, more than 39 s for 7-year-olds, more than 24 s for 8-year-olds, and more than 19 s for 9- to 11-year-olds.

Several studies have investigated the use of the DEM with adults subjects (81–83). Sampedro and colleagues (83) developed an adult version called the Adult Developmental Eye Movement Test (A-DEM). This version was developed with norms for Spanish speakers aged 14 to 68 years. The A-DEM is similar to the DEM with two exceptions: First, the A-DEM uses double-digit numbers as test stimuli rather than the single-digit numbers on the DEM. Second, the numbers used for the horizontal array are not the same as those in the vertical array as they are on the DEM. It is not clear whether the norms developed for the Spanish-speaking population can be used for English-speaking patients. Given the high prevalence of eye movement problems after traumatic brain injury in adults (84–87), it would be valuable to further develop an adult version of the DEM for this population.