Dysfunction of dynamic visual acuity in school children with learning difficulties

The article discusses the results of the dynamic visual acuity test in children aged 5–15 with learning difficulties. Dynamic acuity is a parameter that reflects the correlation between the vestibular and oculomotor systems. One of the functions of the vestibular system is automatic eye-ball stabilization during head movements. This mechanism allows to keep the picture stable on the eye’s retina, which makes visual perception possible. To test visual acuity of test subjects we used the standard table by Sivtsev or LEA symbols table under two conditions. The first condition (static visual acuity): the test subject was sitting still with no head movement and naming the letters or symbols that the tester showed. The second condition (dynamic visual acuity): the test subject was making quick head movements from side to side with the frequency of 2 Hz and naming the symbols the tester showed. Under normal conditions, due to vestibular ocular reflex which occurs in response to quick head movements, dynamic visual acuity and static visual acuity do not show much difference. The difference is no more than one line on the visual acuity chart. The research involved 174 children with learning difficulties. It was found that 37% of the study participants had impaired dynamic visual acuity. Impairment of dynamic visual acuity is connected with hyporeactivity of semicircular canals of the vestibular system which results in low efficiency of the vestibular ocular reflex. This dysfunction may explain the difficulties in the automation of reading in children — reading requires additional energy resources a child has to allocate to stabilize eye balls and recognize figures. This simple test is easy to administer in any educational facility. It allows to detect at-risk children who must do special exercises to develop dynamic visual acuity.