The Developmental Eye Movement Test Does Not Detect Oculomotor Problems: Evidence from Children with Nystagmus

The Developmental Eye Movement (DEM) test, a test purported to assess oculomotor skills, does not detect eye movement disorder in nystagmus syndromes. The test should not be used for the clinical evaluation of oculomotor disorders. PURPOSE: The DEM test ratio compares a horizontal number naming subtest with a vertical one to identify oculomotor problems independent of a child's visual-verbal naming skills. Here, we tested the construct validity of this method by comparing scores of children with and without pathologic nystagmus. Such a nystagmus disturbs normal fixation and saccadic behavior because of the presence of involuntary rhythmic oscillations of the eyes. Therefore, if the ratio is indeed a comprehensive measure of oculomotor problems, children with nystagmus should show an increased ratio score. METHODS: The DEM test performances of normally sighted children (n = 94), children with ocular visual impairments (VI(o); n = 33), and children with cerebral visual impairment (n = 30) were analyzed using linear regression. Part of the children with VI(o) and cerebral visual impairment had either fusion maldevelopment nystagmus syndrome (n = 8) or infantile nystagmus syndrome (n = 20), whereas the others showed no pathologic nystagmus. RESULTS: The times needed for the horizontal and vertical subtests were significantly different between children with normal vision, VI(o), and cerebral visual impairment (P < .001). However, the presence of nystagmus did not add significantly to the horizontal and vertical times (P > .20), nor did it have an effect on the ratio (P > .10). CONCLUSIONS: The DEM test ratio is not sensitive to fixation and saccade abnormalities associated with nystagmus, indicating that it does not have general construct validity to detect true eye movement disorders. Although not suitable for the evaluation of oculomotor disorders, the subtests do have clinical relevance in the diagnosis of cerebral visual impairment.