Comparison of children with and without dyslexia using functional head impulse test and pediatric balance scale

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Originally posted at Frontiers in Neurology by Gül Ölçek / June 02, 2023

Purpose: The aim of this study is to compare functionality of vestibulo-ocular reflex (VOR) responses to evaluate the functional properties of the vestibular system and daily balance performance in children with dyslexia and children with normal development.

Method: Fifteen participants diagnosed with dyslexia were included in the study group (SG), and 15 healthy participants were included in the control group (CG). All groups underwent Functional Head Impulse Test (f-HIT) and Pediatric Balance Scale (PBS). f-HIT was performed with at least 15 head impulses at 4000-5000-6000°/s² randomly to the right and left in the plane of the horizontal semicircular canal (SCC). Statistical analysis was performed using descriptive statistics and the Mann-Whitney U test.

Results: SG percentage values were obtained lower than CG percentage values. Comparisons between the two groups showed that there was a significant difference in all parameters (4000-5000-6000°/s² and total) in the right-side stimulation, there was significant difference for 4,000 s² and total correct answers in the left side. In addition, although there was no significant difference between the groups in terms of the PBS score, the SG scores were lower (p = 0.062).

Conclusions: As a novel test, f-HIT, revealed the difference in functionality of vestibular performance in the dyslexia group. In the dyslexia group, f-HIT may be helpful in evaluating and monitoring the vestibular system.

1. Introduction

Specific learning disorder (SLD) is a neurodevelopmental disorder characterized by persistent difficulties in many areas, such as reading, writing, mathematics, listening, speaking, and reasoning, thus poor performance in learning and academic skills for the expected age (1, 2). SLD can be characterized by impaired academic skills despite intact vision, intact hearing, chronological age-appropriate intelligence and education (1, 3). SLD can be subdivided into dyslexia (difficulty in reading and language), dyscalculia (difficulty in mathematics) and dysgraphia (difficulty in writing) according to the difficulty experienced by the person.

The most prominent theory about origin of dyslexia proposes that cognitive deficiencies in phonological processing, which can be defined as ability to decode and manipulate phonemes or difficulty associating letters with the appropriate sounds (4–7). In addition to phonological and literacy difficulties in dyslexia, many studies have focused on the effects of the cerebellum and its functions (8–10). The cerebellum could contribute to reading in various aspects, including eye movements, language and spatial processing, working memory, and skill acquisition and automaticity (8). Thus, while cerebellar dysfunction is not likely the primary cause of dyslexia, impairments on cerebellar tasks—including eye movement control, postural stability, and implicit motor learning could be shown in children and adults with dyslexia (9). Moreover, vestibulo-cerebellar dysfunction can be addressed in the dyslexia group because the cerebellum is inextricably linked to the vestibular system (11, 12). Therefore, altered vestibular function may exist in this group, which may contribute to balance and gait disturbances (13).

It has been reported that children with dyslexia have worse postural performance than children with normal development (14–16). Poor postural performance in children with dyslexia may be due to impairment in visual, proprioceptive, and vestibular systems or to the integration of these sensory cues that contribute to appropriate motor activity (16, 17). For this reason, it is important to evaluate posture, gait, general motor skills, and balance skills in children with dyslexia.

The vestibular system produces reflexes that are crucial for stabilizing the visual axis (gaze) and maintaining head and body posture (18). When the head rotates with angular velocity in the horizontal and vertical (anterior and posterior SCCs) planes, eye movement occurs in the opposite direction to that of the head (19). This reflex, called the VOR, stabilizes the image on the retina during rapid head movements and can be measured utilizing the vestibular testing approaches such as the head impulse test (HIT) (19). The fixation of an image on the fovea is mainly based on the activity of the vestibular and visual systems (20). The activity of each of these systems varies according to the frequency of head movement. For example, at low frequencies (< 0.1 Hz), the visual system is dominant; at mid frequencies, the vestibular and visual systems interact together to stabilize the gaze; at high frequencies (between 1 and 5 Hz), only the vestibular system is activated (21).

Halmagyi and Curthoys described rapid horizontal head rotation, Head Impulse Test (HIT), to use as an important clinical screening (22). The use of this test has increased with the development of a high-speed video HIT system (vHIT). vHIT is easy to use as a clinical tool and has been validated as a diagnostic test of semicircular canal function (23). While the vHIT provides a gain value that summarizes the behavior of the VOR, another similar test, f-HIT, provides data on the ability to recognize the orientation of a Landolt C optotype (24). While vHIT does not provide direct information on the functional effectiveness of the motor response, f-HIT is a functional measure of the VOR as it measures the ability to read and maintain clear vision during head movement (24). Thus, f-HIT can provide information about the vestibular system by providing a functional measurement of the VOR. In the test, the individual is asked to identify an optotype presented briefly during passive head impulses in each SCC plane, and the percentage of correct responses is recorded.

The aim of this study was to compare functional VOR responses and balance skills using f-HIT and PBS in children with dyslexia and children with normal development. In the current study, two specific hypotheses were tested:

i. Children with dyslexia will show worse results in terms of static and dynamic balance in PBS than children with normal development.

ii. Children with dyslexia will show worse results in terms of functional VOR in f-HIT than children with normal development.

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