Developmental Eye Movement (DEM) Test
Purpose and Clinical Application
The Developmental Eye Movement (DEM) test is a practical screening tool that assesses ocular motor skills and rapid automatized naming in children, particularly useful for evaluating vision-related reading problems, though it has significant limitations in detecting true oculomotor disorders. 1
What the Test Measures
The DEM test evaluates eye movement performance through a structured number-naming task:
- Vertical subtest: Children read numbers arranged in vertical columns 1
- Horizontal subtest: Children read numbers arranged in horizontal lines 1
- Ratio calculation: Compares horizontal to vertical performance to identify oculomotor dysfunction independent of visual-verbal naming skills 2
The test measures an aspect of eye movement related to reading rather than purely assessing eye movement parameters themselves 1. Performance on the DEM correlates with symptoms associated with oculomotor dysfunction, with failing the DEM Ratio identifying 90% of symptomatic subjects 3.
Clinical Indications
The DEM test is appropriate when:
- Evaluating children with reading concerns, as part of assessing accommodation and convergence, which can be helpful in children presenting with reading difficulties 4
- Screening for vision-related visual problems requiring rapid assessment of eye movement 1
- Diagnosing cerebral visual impairment (CVI), particularly when combined with crowding assessment, as children with CVI need significantly more time to read horizontal DEM numbers compared to those with isolated visual impairment 5
Important Limitations and Pitfalls
The DEM test does not detect true oculomotor disorders: Research demonstrates that children with pathologic nystagmus (fusion maldevelopment nystagmus syndrome or infantile nystagmus syndrome) show no significant difference in DEM ratio scores compared to children without nystagmus, despite having clear fixation and saccadic abnormalities 2. This indicates the test lacks construct validity for evaluating genuine eye movement disorders and should not be used for clinical evaluation of oculomotor problems 2.
Additional concerns include:
- Learning effect: Repeatability is compromised by learning effects over multiple sessions, requiring awareness for correct clinical interpretation 1
- Test-retest reliability varies by setting: Better reliability occurs in office settings with patients undergoing vision therapy evaluation compared to school-based screening 3
- Limited specificity: Children with developmental coordination disorder (DCD) show only mild atypical performance, while children with developmental dyslexia (DD) demonstrate particularly poor performance, suggesting the test is more sensitive to reading-related difficulties than pure motor dysfunction 6
Treatment Approach Based on Findings
When DEM testing reveals abnormalities:
Refer for comprehensive ophthalmologic evaluation if the child shows poor performance, as this may indicate underlying accommodative or convergence insufficiency (present in 2-6% of 5th-6th graders for convergence insufficiency and 10% for accommodative insufficiency) 4
Assess accommodation and convergence directly through testing near point of accommodation and convergence, and determining accommodative and fusional convergence amplitudes 4
Consider noncycloplegic retinoscopy for rapid assessment of accommodation, particularly helpful in children with asthenopia and high hyperopia or those at risk for accommodative dysfunction (cerebral palsy, Down syndrome, developmental delay) 4
Do not rely on DEM alone for diagnosing true oculomotor disorders; use eye-tracking techniques or comprehensive sensorimotor evaluation including binocular alignment testing, stereoacuity assessment, and ocular motility assessment 4, 6, 2
Key Clinical Caveat
The DEM test should be viewed as a screening tool for reading-related visual problems rather than a diagnostic test for oculomotor dysfunction 1, 2. When true eye movement disorders are suspected, comprehensive ophthalmologic examination with direct assessment of ocular versions, ductions, and binocular alignment is essential 4.