Vision-laterality analysis in children with reading disability: the results of new techniques of examination

Binocular coordination of children with dyslexia and typically developing children in linguistic and non-linguistic tasks: evidence from eye movements

Given the increased evidence suggesting the presence of binocular coordination deficits in dyslexia, investigations of binocular eye movements are beneficial to clarify the underlying causes of reading difficulties. This systematic review aims to (a) synthesize the literature through the examination of binocular coordination in children with dyslexia by describing the normative development of stable binocular control and (b) outline future directions. Boolean expressions in the PubMed search were used to define papers. Following a literature search and selection process, 25 papers were included. Studies using binocular eye tracking during linguistic and nonlinguistic tasks in children with dyslexia and typical development 5-17 years of age are reviewed. The studies reviewed provided consistent evidence of poor binocular coordination in children with dyslexia, but the results associated with different task characteristics were less consistent. The relation between binocular coordination deficits and reading difficulties needs to be further elucidated in longitudinal studies which may provide future treatments targeting the binocular viewing system in dyslexia.

Is crossed laterality associated with academic achievement and intelligence? A systematic review and meta-analysis

Over the last century, sporadic research has suggested that people whose hand, eye, foot, or ear dominances are not consistently right- or left-sided are at special risk of suffering academic difficulties. This phenomenon is known as crossed laterality. Although the bulk of this research dates from 1960's and 1970's, crossed laterality is becoming increasingly popular in the area of school education, driving the creation of several interventions aimed at restoring or consolidating lateral dominance. However, the available evidence is fragmentary. To determine the impact of crossed laterality on academic achievement and intelligence, we conducted a systematic review and meta-analysis of articles published since 1900. The inclusion criteria for the review required that studies used one or more lateral preference tasks for at least two specific parts of the body; they included a valid measure of crossed laterality; they measured the impact of crossed laterality on academic achievement or intelligence; and they included participants between 3 and 17 years old. The final sample included 26 articles that covered a total population of 3578 children aged 5 to 12. Taken collectively, the results of these studies do not support the claim that there is a reliable association between crossed laterality and either academic achievement or intelligence. Along with this, we detected important shortcomings in the literature, such as considerable heterogeneity among the variables used to measure laterality and among the tasks utilized to measure the outcomes. The educational implications of these results are discussed.

The prevalence of optometric anomalies and symptoms in children receiving special tuition

A case-control study was performed where 9 pupils receiving special tuition (ST-group) were compared with 36 controls. Six (66.7%) of the pupils in the ST-group were diagnosed as dyslexic. No significant correlation was revealed between receiving special tuition and having reduced visual function, nor between reduced visual function and number of visually related symptoms. Although the number of symptoms was not significantly greater in the ST-group, some of the symptoms were significantly more common in the ST-group, and none were significantly more common in the control group.

Cognitive processing and self-report of lateral preference

Our knowledge of the human brain has increased more during the past 40 years than at any other time in history. Of particular interest have been the findings of a correspondence between cognitive functions and individual structures of the brain. Similar from a gross anatomical point of view, the hemispheres of the brain have been shown to serve specialized cognitive functions. This work offers an overview of the cognitive aspects of cerebral lateralization as a context for considering this issue, followed by a review of specific self-report techniques in the appraisal of lateral preference.

Effects of eye muscle proprioceptive activation on eye position in normal and exotropic subjects

BACKGROUND

Activation of muscle spindles by vibration of eye muscles is known to induce illusory movements of fixated targets, but the effects on eye position have not been studied, either in normal subjects or in patients with exotropia.

METHODS

Eye position was recorded from the covered, non-dominant eye with an infrared system in 11 subjects with normal eyes and binocular vision and in 10 patients with exotropia and abnormal binocular function. Activation of eye muscle spindles was done by vibration at 70 Hz of the inferior and lateral rectus muscles of the dominant eye, fixating a light-emitting diode in subdued light.

RESULTS

Vibratory activation of proprioceptors in the inferior rectus muscle induced an eye movement mainly directed upward in both normal and exotropic subjects. The magnitude of the movement was on average 2.7 deg in normals and 2.4 deg in exotropes. Lateral rectus vibration induced a movement that was mainly temporally directed (abduction) of an average 2.1 deg in normal subjects, but a nasally directed (adduction) movement of 4.2 deg in exotropic subjects. In normal subjects the eye movement is of the same direction as the earlier reported visual illusory movements induced by the same type of proprioceptive activation, but in exotropic subjects the movements is in the opposite direction.

CONCLUSIONS

Proprioceptive activation of eye muscles affects eye position, and the results also indicate that signals from eye muscles are processed differently in normals and strabismics, probably depending on the level of binocular function.

The neuropsychological significance of lateral preference for complex visual activities in children with learning disabilities

In the present study the relationship between neuropsychological functioning and lateral preference for visual activities was examined with learning disordered children. Specifically, the relationship between measures of the Lateral Dominance Exam (LDE), scores on the Halstead-Reitan Neuropsychological Battery (HRNB), and the Wechsler Intelligence Scale for Children-Revised (WISC-R) were explored. A canonical analysis suggested that composites of neuropsychological functioning and lateral preference shared 22% of variance. Learning disabled children with strong right or left preference for visually guided motor activities showed lower performance in spatial tasks on the ipsilateral side and in simple motor skills on the contralateral side. Children in the present study with strong right preference patterns for visually assisted motor activities also showed low performance on visual tracking tasks. These data offer some support for assessing lateral preference in learning disabled children.

Dynamics of accommodative vergence movements controlled by the dominant and non-dominant eye

Accommodative vergence responses to accommodative stimuli presented at three different amplitudes in a stepwise and a sinusoidal mode to either the dominant or the non-dominant eye were studied. The motor control loop was opened by one eye viewing the target and the other eye covered. Each eye was stimulated monocularly and eye movements were recorded with an infra-red reflection system. Latency and time constant of the accommodative vergence response to step stimulation or the phase of the vergence response to sine wave stimulation, did not vary systematically with stimulus amplitude or eye stimulated. However, the gain of the accommodative vergence movements was highest in the non-dominant eye at a particular stimulus amplitude. This suggested that accommodative vergence angles can vary depending on which eye is leading and driving the accommodative vergence system in a specific fixation situation.

Investigation of accommodative and binocular function in dyslexia

The visual correlates of dyslexia are the subject of controversy, and much evidence suggests that they may include some aspects of binocular and accommodative function. These factors were investigated in 43 control and 39 dyslexic children, who were matched for age, sex and performance intelligence quotient. The dyslexic group exhibited significantly lower positive and negative vergence reserves, and vergence instability when the eyes were dissociated at near. Their amplitudes of accommodation also were significantly reduced. However, other measures including dissociated and associated heterophoria and accommodative lag and facility were similar in both groups. The stability of motor ocular dominance, as assessed with a modified Dunlop test, was similar in both groups. The results of a simulated reading visual search task suggested that the vergence and accommodative dysfunction were not a major cause of the dyslexia. Further analyses, using reading-age matched groups, suggested that these ocular motor correlates were not attributable to the better reading performance in the control group. The most likely remaining explanation is that they are, in most cases, non-causal correlates of the dyslexia.

Dyslexia; ophthalmological aspects 1991

Dyslexia or specific reading disability is an important and frequent handicap afflicting 5-10% of the population. It is basically a disorder of acquisition of written language, probably due to a poorly developed phonological awareness, which in turn may be neurologically related. As anatomical correlates symmetry of the planum temporale and ectopies in the cerebral cortex have been suggested. Functional correlates are discovered with brain electrical mapping and stimulation of brain structures during neuro surgery. From an ophthalmological point of view there are no relations between dyslexia and ocular problems including refractive errors and accommodation, problems of binocular control and stereopsis, eye dominance instability etc. However, contrast sensitivity seems to be reduced in dyslexics for the middle range of spatial frequencies, which may be related to impaired function of the 'transient' visual system. With regard to eye movements, there is no firm experimental proof for any disturbances in dyslexia, be it with the different movement systems or in the best movement direction. 'Backward saccades' or regressions are typical not only for dyslexic reading but in all types of reading when comprehension is poor. Although there is no treatment for dyslexia itself that can be based on ophthalmological findings, the ophthalmologist must after careful examination discover and treat any ocular, orthoptic or neuroophthalmological problem that may make reading difficult for the dyslexic child. The ophthalmologist must explain to the child and the parents that dyslexia usually has no ophthalmological or visual cause but is a disability with a neurobiological background, still unknown, in which the only efficient treatment is within the area of pedagogy.

Unfixed reference, monocular occlusion, and developmental dyslexia--a critique

Stein and Fowler have proposed that poor binocular control of vergence eye movements is responsible for reading problems in a subset of dyslexic children, and that this subgroup is characterised by unstable performance on Dunlop's reference eye test. Four predictions from this hypothesis are evaluated in the light of published evidence. First, it is shown that a substantial minority of good readers have unfixed reference. Second, the evidence for a raised prevalence of unfixed reference in dyslexics is reviewed and contradictory findings are discussed. Third, it is argued that there is little support for the view that dyslexics with unfixed reference make different types of reading errors from those with fixed reference: indeed many dyslexics with unfixed reference have non-visual, phonological difficulties. Finally, it is argued that studies which claim that monocular occlusion is a successful treatment for 'visual dyslexia' are methodologically flawed and do not provide convincing evidence for this view.

Laterality and reading attainment

This investigation was concerned with measures of laterality and their usefulness as predictors of reading attainment. Previous research has suggested that retarded reading is the result of abnormal development of cerebral dominance, and that this may be indicated by left-handedness or by inconsistencies in lateral preference. A group of schoolboys carried out tests of lateral preference, reading, spelling, and experimental tasks involving dichotic listening and tachistoscopic recognition. There was no evidence that left-handedness, right cerebral dominance, or inconsistencies in laterality were correlated with reading retardation.

Orthoptic status and reading disability

147 unselected 8-year-olds were given tests of intelligence, reading ability and orthoptic status, including the reference eye test described by Dunlop, Dunlop and Fenelon (1973). We failed to replicate their findings of a raised incidence of convergence deficiency, defective stereopsis and esophoria in children with specific reading disability. Furthermore, in contrast to their results, we found that crossed reference (i.e. reference eye on opposite side to preferred hand) was common in this sample and not associated with reading problems.