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Can vergence training improve reading in dyslexics?
Abstract
Background:
Dyslexia affects 5%-8% of the population of the Western world. While reading, different eye movements are required. Compared to other persons, dyslexics have more and longer fixations, shorter saccade amplitude, a higher percentage of regression, and more fixation disparity when reading. In non-reading situations, dyslexics do not have more binocular problems than others. The aim of the present study was to investigate whether computerized orthoptic vergence training could improve reading ability for dyslexic children.
Methods:
The study was conducted at Ängkärrskolan, Solna, an elementary school exclusively for dyslexic children. Twelve subjects, aged 13-14 years, were trained with RetCorr, a computerized vergence training program. Reading speed was assessed before and after treatment. The results were compared with an age-matched control group.
Results:
The dyslexic subjects conducted on average 11.75 sessions (±2.53 SD) of orthoptic training over a 5-week period. On average, the number of words read per minute before training were 87.83 (±16.80 SD) and after training 95.58 words (±18.08 SD). The difference was statistically significant (p=0.0066). In the control group, the change was from 85.00 (±19.68 SD) words to 89.37 words (±19.71 SD) over the same time period. This difference was not significant (p=0.1235).
Discussion:
Most scientists agree that dyslexia is mainly a phonological impairment. Nevertheless, the results show that vergence treatment might help dyslexics. Larger studies are required to provide guidance in this area.
... (Table 4 )showing a notable difference in many studies on NPC in dyslexic population. 3,5,10,[19][20][21][22]26 A possible explanation for these difficulties could be that dyslexia is associated with underlying neurological and cognitive differences. These differences may include problems with visual processing and attention. ...
... 5,19,25,27 amplitude of accommodation was observed to be significantly decreased in dyslexic group in comparison with normal child population group and contrasting results were seen in other studies where no difference was seen. 3,16,17,22,24 altogether studies are compiled in (Table 7 ). ...
... The mean distance from the point of convergence was found to be reduced in most of the studies for the "dyslexic" group in comparison with the control groups. 3,5,10,[19][20][21][22]26 Similar seen in the convergence insufficient population (p= 0.027). 21 The study also found that the NPC break and recovery varied considerably across children in kindergarten, third grade, and sixth grade, suggesting that the age of the dyslexic population should also be taken into account when diagnosis. ...
Based on a qualitative study of a broad and varied body of literature, this review of literature reveals the potential roles of accommodation and vergence in children with dyslexia. With a thorough literature study, this review of literature aims to provide an all-encompassing perspective on the binocular vision parameters in children with dyslexia and its significance in clinical practice in this review, addressing the lack of a comprehensive study in this area. By summarizing the latest research, this article is a valuable resource for researchers, clinicians, educators, and individuals interested in comprehending the relationship between dyslexia and binocular vision and exploring potential connections and implications. Both original and review papers were examined by searching research databases from 1991 to 2022, including PubMed, Google Scholar, and Ovid. The ROBINS-I risk of bias assessment approach for non-randomized trials was used to evaluate the quality of the included papers. This review includes a total of eighteen articles. Because only the dyslexic population was studied in this study, all of the studies were non-randomized. Changes in Ocular parameters, the function of Accommodation, and Vergence in the dyslexic population were observed and included in this study. This review of literature provides educators and clinicians with crucial insights and awareness to enhance their understanding of the parameters associated with non-strabismic binocular vision disorders in children with dyslexia, as well as strategies for detection. Evidence-based guidelines can be created for controlling and assessing binocular vision parameters in children with dyslexia and their importance in clinical practice.
... More recently, eye movement abnormalities in dyslexic adolescents have been demonstrated using more objective measurements, some resulting in increased latencies of both vergence and saccadic movements 11,17,20,21 . There has even been evidence to show that vergence training may improve reading in dyslexic adolescents (increased number of words read per minute), indicating there is a basis of vergence abnormality to their primary deficit 22 . However, these studies have been conducted on only a small sample size, some of them using targets that cover only a small range of movement, which does not replicate how dyslexics would view larger targets in real life. ...
... The present study. To date, many clinical studies have suggested vergence and accommodation difficulties in dyslexics without objective evaluation [16][17][18]22 . Other studies suggest eye movement deficits during reading in dyslexics, including larger amplitudes, longer fixations, frequent regressive saccades, problems coordinating movement to the next line, and poor binocular coordination during saccades and fixations [10][11][12][13]32 . ...
Previous studies suggest vergence and saccade abnormalities in dyslexic adolescents. However, these studies are mainly clinically based and do not provide objective measurements of eye movements, but rather subjectively evaluate vergence using haplosopic conditions in which the two eyes are dissociated (via polarizers, prisms, or intermittent spectacles). Other studies have identified deficits with binocular coordination during reading in dyslexics. Yet, there are few studies that provide objective measurements of eye movements in the dyslexic population to help provide more information regarding if these deficits could be due to an intrinsic motor problem or if they are the consequence of poor reading. 47 dyslexic adolescents (18 female, 29 male; mean age 15.5) and 44 non-dyslexic adolescents (22 female, 22 male; mean age 14.8) wore a head-based eye tracker (PupilCore, Pupil Labs, Berlin) which recorded wide angle saccade and vergence eye movements at 200 Hz. Tests were run using the REMOBI device, which produced a saccade or vergence audiovisual target. Analysis of eye movements was performed with lab-developed software, AIDEAL. The results showed statistically significant abnormalities in vergence and saccades. In vergence, dyslexics displayed a reduced amplitude of the visually driven portion of convergence and a longer duration in the initial phase of divergence. In saccades, dyslexic adolescents demonstrated slower saccades in both directions. They also had an increased disconjugate drift in the first 80 or 160 ms following saccades to the right, suggesting poor binocular coordination. For both vergence and saccades, the peak velocity and time to peak velocity was higher and earlier, respectively, in non-dyslexics compared to dyslexics; yet the average velocity of both movements was lower in dyslexics. Thus, these results indicate peculiar velocity profiles in dyslexics, particularly a slow deceleration phase in both vergence and saccades. The study provides an objective method to diagnose vergence and saccade abnormalities while viewing targets in the real three-dimensional space in a dyslexic population. Vergence abnormalities are demonstrated to be a problem in dyslexics, occurring independently from reading. We hypothesize these disconjugate drifts following saccades are the result of slow vergence capacity. Rehabilitation programs, such as those using REMOBI, should aim to target these deficits in vergence velocity, as this has been shown to improve binocular control.
... The effectiveness of dynamic computer visual attentional interventions in enhancing the reading abilities of children with DD has been documented [34]. Additionally, eye vergence training through computer games has been shown to benefit the reading skills of children with DD [35]. ...
To evaluate the effect of online visual games on the balance, visual perception, and oculomotor skills of children with developmental dyslexia during the COVID-19 pandemic.
In this single-blind randomized clinical trial, 50 children with developmental dyslexia, aged 7 to 11 years, were recruited from rehabilitation centers in Tehran, Iran, using a convenience sampling strategy. Participants were randomly divided into two groups: intervention (25) and control (25), with close matching based on sex, age, IQ, and type of disease. The interventions consisted of web-based online computer games focusing on visual perception and oculomotor skills. Outcome measures included the Test of Visual Perception Skills—Revised, the Pediatric Balance Scale, and videonystagmography. The Wechsler Intelligence Scale for Children—IV and the Reading and Dyslexia Test were used to evaluate IQ and reading skills, respectively.
The intervention group exhibited significant post-intervention improvements in the Test of Visual Perception Skills—Revised, tracking gain, saccade latency, and saccade velocity scores (all P < 0.001). In contrast, the control group showed no significant differences in these tests in pre- and post-intervention (all P > 0.05). Notably, post-intervention comparisons between the groups revealed significant differences in smooth pursuit eye movements (P < 0.001), saccade latency (P = 0.027), and saccade velocity (P < 0.001). The Pediatric Balance Scale scores remained unchanged in both groups post-intervention (intervention: P = 0.317; control: P = 0.999). Game face validity was affirmed with impact scores above 1.5 for all items, suggesting that the games were straightforward, clear, and relevant.
Online visual games enhanced oculomotor and visual perception skills in children with dyslexia but did not influence balance skills.
... Diplopia thresholds increased in magnitude only in the Convergence load High subcategory of participants (as evident in the pre-and post-task comparisons). Analogous to the findings presented by Ramsay et al. (2014), the increased dlPFC oxygenation over time may be caused by short-term activitydependent plasticity and learning in a network for oculomotor control subservient of convergence/divergence coordination eyemovements of which the dlPFC plays a part. In this scenario, the dlPFC increased its metabolic demands over time because of a systematic increase in tonic discharge of cortical neurons, the increased recruitment of cortical cells, and an increase in their firing rate. ...
Purpose: To extend our knowledge of the functional linkages between visual fatigue and regional cerebral prefrontal cortex (PFC) oxygenation, we measured time related hemodynamic changes over the right dorsolateral prefrontal cortex (dlPFC) during convergence load under conflicting stimulus-to-accommodation and stimulus-to-vergence eye movements with and without concurrent mental load.
Methods: Twenty healthy participants with a median age of 28 years (range: 18–44 years) fixated upon a vertical bar presented separately to the left and right eyes, using polarized filters, during four counterbalanced 10-min periods: (i) no accommodation/vergence conflict (Control, Ctrl); (ii) added convergence load and accommodation/vergence conflict (Conv); (iii) added cognitive load only (Cog) and; (iv) a combination of added cognitive and convergence load and accommodation/vergence conflict (Cc). Viewing distance was 65 cm. Non-invasive measurements of hemodynamic activity over the dlPFC were quantified by functional near-infrared spectroscopy (fNIRS). During the two-convergence load conditions, the horizontal disparity of the two bars varied dynamically from no disparity to a disparity set 20% below the individual threshold for diplopia. Cognitive load was induced by the n-back-2 test which required the subject to memorize and recall the changing colors of the horizontal bars and decide when a given color was the same as that occurring two colors previously. fNIRS data were averaged over 10-s windows centered at 0, 2, 4, 6, 8, and 10 min of each task, subtracted from a 20-s baseline window immediately preceding the visual task, and then represented as changes in oxygenated hemoglobin (ΔHbO2), deoxygenated hemoglobin (ΔHHb) and total hemoglobin (ΔtHb).
Results: Linear mixed model analyses showed that hemodynamic activity was systematically influenced by time (p < 0.001). The group-averaged time-related level of change across the viewing conditions did not differ when compared with one another (p > 0.05). Larger convergence eye-movement responses under conflicting stimulus-to-accommodation, and stimulus-to-vergence over time, increased ΔHbO2 and ΔtHb only in condition Cc and after 8 min of task time (p < 0.10 for min⁻⁶ and min⁻⁸: p < 0.05 for min⁻¹⁰).
Discussion: Collectively, our data suggest that HbO2, HHb, and tHb, recorded over the dlPFC with fNIRS, can be used to assay the degree to which supervisory oculomotor control processes are activated during visually deficient near work.
Poor response to treatment is a defining characteristic of reading disorder. In the present systematic review and meta-analysis, we found that the overall average effect size for treatment efficacy was modest, with a mean standardized difference of 0.38. Small true effects, combined with the difficulty to recruit large samples, seriously challenge researchers planning to test treatment efficacy in dyslexia and potentially in other learning disorders. Nonetheless, most published studies claim effectiveness, generally based on liberal use of multiple testing. This inflates the risk that most statistically significant results are associated with overestimated effect sizes. To enhance power, we propose the strategic use of repeated measurements with mixed-effects modelling. This novel approach would enable us to estimate both individual parameters and population-level effects more reliably. We suggest assessing a reading outcome not once, but three times, at pre-treatment and three times at post-treatment. Such design would require only modest additional efforts compared to current practices. Based on this, we performed ad hoc a priori design analyses via simulation studies. Results showed that using the novel design may allow one to reach adequate power even with low sample sizes of 30–40 participants (i.e., 15–20 participants per group) for a typical effect size of d = 0.38. Nonetheless, more conservative assumptions are warranted for various reasons, including a high risk of publication bias in the extant literature. Our considerations can be extended to intervention studies of other types of neurodevelopmental disorders.
Background:
Convergence insufficiency is a common binocular vision disorder in which the eyes have a strong tendency to drift outward (exophoria) with difficulty turning the eyes inward when reading or doing close work.
Objectives:
To assess the comparative effectiveness and relative ranking of non-surgical interventions for convergence insufficiency through a systematic review and network meta-analysis (NMA).
Search methods:
We searched CENTRAL, MEDLINE, Embase, PubMed and three trials registers up to 20 September 2019.
Selection criteria:
We included randomized controlled trials (RCTs) examining any form of non-surgical intervention versus placebo, no treatment, sham treatment, or other non-surgical interventions. Participants were children and adults with symptomatic convergence insufficiency.
Data collection and analysis:
We followed standard Cochrane methodology. We performed NMAs separately for children and adults.
Main results:
We included 12 trials (six in children and six in adults) with a total of 1289 participants. Trials evaluated seven interventions: 1) office-based vergence/accommodative therapy with home reinforcement; 2) home-based pencil/target push-ups; 3) home-based computer vergence/accommodative therapy; 4) office-based vergence/accommodative therapy alone; 5) placebo vergence/accommodative therapy or other placebo intervention; 6) prism reading glasses; and 7) placebo reading glasses. Six RCTs in the pediatric population randomized 968 participants. Of these, the Convergence Insufficiency Treatment Trial (CITT) Investigator Group completed four RCTs with 737 participants. All four CITT RCTs were rated at low risk of bias. Diagnostic criteria and outcome measures were identical or similar among these trials. The four CITT RCTs contributed data to the pediatric NMA, incorporating interventions 1, 2, 3 and 5. When treatment success was defined by a composite outcome requiring both clinical measures of convergence to be normal, and also show a pre-specified magnitude of improvement, we found high-certainty evidence that office-based vergence/accommodative therapy with home reinforcement increases the chance of a successful outcome, compared with home-based computer vergence/accommodative therapy (risk ratio (RR) 1.96, 95% confidence interval (CI) 1.32 to 2.94), home-based pencil/target push-ups (RR 2.86, 95% CI 1.82 to 4.35); and placebo (RR 3.04, 95% CI 2.32 to 3.98). However, there may be no evidence of any treatment difference between home-based computer vergence/accommodative therapy and home-based pencil/target push-ups (RR 1.44, 95% CI 0.93 to 2.24; low-certainty evidence), or between either of the two home-based therapies and placebo therapy, for the outcome of treatment success. When treatment success was defined as the composite convergence and symptom success outcome, we found moderate-certainty evidence that participants who received office-based vergence/accommodative therapy with home reinforcement were 5.12 (95% CI 2.01 to 13.07) times more likely to achieve treatment success than those who received placebo therapy. We found low-certainty evidence that participants who received office-based vergence/accommodative therapy with home reinforcement might be 4.41 (95% CI 1.26 to 15.38) times more likely to achieve treatment success than those who received home-based pencil push-ups, and 4.65 (95% CI 1.23 to 17.54) times more likely than those who received home-based computer vergence/accommodative therapy. There was no evidence of any treatment difference between home-based pencil push-ups and home-based computer vergence/accommodative therapy, or between either of the two home-based therapies and placebo therapy. One RCT evaluated the effectiveness of base-in prism reading glasses in children. When base-in prism reading glasses were compared with placebo reading glasses, investigators found no evidence of a difference in the three outcome measures of near point convergence (NPC), positive fusional vergence (PFV), or symptom scores measured by the Convergence Insufficiency Symptom Survey (CISS). Six RCTs in the adult population randomized 321 participants. We rated only one RCT at low risk of bias. Because not all studies of adults included composite success data, we could not conduct NMAs for treatment success. We thus were limited to comparing the mean difference (MD) between interventions for improving NPC, PFV, and CISS scores individually using data from three RCTs (107 participants; interventions 1, 2, 4 and 5). Compared with placebo treatment, office-based vergence accommodative therapy was relatively more effective in improving PFV (MD 16.73, 95% CI 6.96 to 26.60), but there was no evidence of a difference for NPC or the CISS score. There was no evidence of difference for any other comparisons for any outcomes. One trial evaluated base-in prism glasses prescribed for near-work activities and found that the prism glasses group had fewer symptoms compared with the placebo glasses group at three months (MD -8.9, 95% CI -11.6 to -6.3). The trial found no evidence of a difference with this intervention in NPC or PFV. No adverse effects related to study treatments were reported for any of the included studies. Excellent adherence was reported for office-based vergence/accommodative therapy (96.6% or higher) in two trials. Reported adherence with home-based therapy was less consistent, with one study reporting decreasing adherence over time (weeks 7 to 12) and lower completion rates with home-based pencil/target push-ups.
Authors' conclusions:
Current research suggests that office-based vergence/accommodative therapy with home reinforcement is more effective than home-based pencil/target push-ups or home-based computer vergence/accommodative therapy for children. In adults, evidence of the effectiveness of various non-surgical interventions is less clear.
Developmental dyslexia (DD) is a heritable condition associated with reading, visual and auditory deficits. Atypical processes involved in low-level sensory coding have been implicated. We tested the contribution made by auditory magnocellular function using a behavioural task which considered the temporal difference between pairs of identical sinewave tones. Adult undergraduates with an existing diagnosis of DD (n = 78) were compared with controls (n = 111) from the same population on error rates and response times at different interval durations. Error rates and response times increased in both groups with increasing task difficulty. However, on average the DD group made uniformly more errors and slower decisions than controls. Unsupervised learning of error patterns exposed a trait continuum associated with individual differences in response efficiency. Difficulty in using temporal information in DD arising from impaired sensory coding in the auditory thalamus is suggested. The results provide strong support for the idea that auditory processing difficulties in dyslexia, along with visual and sensorimotor deficits, have a common neurodevelopmental cause.
Background:
Approximately one in ten students aged 6 to 16 in Ontario (Canada) school boards have an individual education plan (IEP) in place due to various learning disabilities, many of which are specific to reading difficulties. The relationship between reading (specifically objectively determined reading speed and eye movement data), refractive error, and binocular vision related clinical measurements remain elusive.
Methods:
One hundred patients were examined in this study (50 IEP and 50 controls, age range 6 to 16 years). IEP patients were referred by three local school boards, with controls being recruited from the routine clinic population (non-IEP patients in the same age group). A comprehensive eye examination was performed on all subjects, in addition to a full binocular vision work-up and cycloplegic refraction. In addition to the cycloplegic refractive error, the following binocular vision related data was also acquired: vergence facility, vergence amplitudes, accommodative facility, accommodative amplitudes, near point of convergence, stereopsis, and a standardized symptom scoring scale. Both the IEP and control groups were also examined using the Visagraph III system, which permits recording of the following reading parameters objectively: (i) reading speed, both raw values and values compared to grade normative data, and (ii) the number of eye movements made per 100 words read. Comprehension was assessed via a questionnaire administered at the end of the reading task, with each subject requiring 80% or greater comprehension.
Results:
The IEP group had significantly greater hyperopia compared to the control group on cycloplegic examination. Vergence facility was significantly correlated to (i) reading speed, (ii) number of eye movements made when reading, and (iii) a standardized symptom scoring system. Vergence facility was also significantly reduced in the IEP group versus controls. Significant differences in several other binocular vision related scores were also found.
Conclusion:
This research indicates there are significant associations between reading speed, refractive error, and in particular vergence facility. It appears sensible that students being considered for reading specific IEP status should have a full eye examination (including cycloplegia), in addition to a comprehensive binocular vision evaluation.
Studies comparing binocular eye movements during reading and visual search in dyslexic children are, at our knowledge, inexistent. In the present study we examined ocular motor characteristics in dyslexic children versus two groups of non dyslexic children with chronological/reading age-matched. Binocular eye movements were recorded by an infrared system (mobileEBT®, e(ye)BRAIN) in twelve dyslexic children (mean age 11 years old) and a group of chronological age-matched (N = 9) and reading age-matched (N = 10) non dyslexic children. Two visual tasks were used: text reading and visual search. Independently of the task, the ocular motor behavior in dyslexic children is similar to those reported in reading age-matched non dyslexic children: many and longer fixations as well as poor quality of binocular coordination during and after the saccades. In contrast, chronological age-matched non dyslexic children showed a small number of fixations and short duration of fixations in reading task with respect to visual search task; furthermore their saccades were well yoked in both tasks. The atypical eye movement's patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an immaturity of the ocular motor saccade and vergence systems interaction.
Children with developmental dyslexia show reading impairment compared to their peers, despite being matched on IQ, socio-economic background, and educational opportunities. The neurological and cognitive basis of dyslexia remains a highly debated topic. Proponents of the magnocellular theory, which postulates abnormalities in the M-stream of the visual pathway cause developmental dyslexia, claim that children with dyslexia have deficient binocular coordination, and this is the underlying cause of developmental dyslexia. We measured binocular coordination during reading and a non-linguistic scanning task in three participant groups: adults, typically developing children, and children with dyslexia. A significant increase in fixation disparity was observed for dyslexic children solely when reading. Our study casts serious doubts on the claims of the magnocellular theory. The exclusivity of increased fixation disparity in dyslexics during reading might be a result of the allocation of inadequate attentional and/or cognitive resources to the reading process, or suboptimal linguistic processing per se.
Reading requires three-dimensional motor control: saccades bring the eyes from left to right, fixating word after word; and oblique saccades bring the eyes to the next line of the text. The angle of vergence of the two optic axes should be adjusted to the depth of the book or screen and--most importantly--should be maintained in a sustained manner during saccades and fixations. Maintenance of vergence is important as it is a prerequisite for a single clear image of each word to be projected onto the fovea of the eyes. Deficits in the binocular control of saccades and of vergence in dyslexics have been reported previously but only for tasks using single targets. This study examines saccades and vergence control during real text reading. Thirteen dyslexic and seven non-dyslexic children read the French text "L'Allouette" in two viewing distances (40 cm vs. 100 cm), while binocular eye movements were measured with the Chronos Eye-tracking system. We found that the binocular yoking of reading saccades was poor in dyslexic children (relative to non-dyslexics) resulting in vergence errors; their disconjugate drift during fixations was not correlated with the disconjugacy during their saccades, causing considerable variability of vergence angle from fixation to fixation. Due to such poor oculomotor adjustments during reading, the overall fixation disparity was larger for dyslexic children, putting larger demand on their sensory fusion processes. Moreover, for dyslexics the standard deviation of fixation disparity was larger particularly when reading at near distance. We conclude that besides documented phoneme processing disorders, visual/ocular motor imperfections may exist in dyslexics that lead to fixation instability and thus, to instability of the letters or words during reading; such instability may perturb fusional processes and might--in part--complicate letter/word identification.
Objective. Latency of eye movements depends on cortical structures while speed of execution and accuracy depends mostly on subcortical brainstem structures. Prior studies reported in dyslexic reader children abnormalities of latencies of saccades (isolated and combined with vergence); such abnormalities were attributed to deficits of fixation control and of visual attention. In this study we examine speed and accuracy characteristics of horizontal eye movements in natural space (saccades, vergence and combined movements) in dyslexic reader children. Methods. Two paradigms are tested: gap paradigm (fixation offset 200 ms prior to target onset), producing shorter latencies, in both non-dyslexic reader and dyslexic reader children and simultaneous paradigm. Seventeen dyslexic reader children (mean age: 12 +/- 0.08 years) and thirteen non-dyslexic reader children (mean age: 12 +/- 1 years) were tested. Horizontal eye movements from both eyes were recorded simultaneously by a photoelectric device (Oculometer, Dr. Bouis). Results. For all movements tested (saccades, vergence, isolated or combined) and for both paradigms, the mean velocity and accuracy were similar in dyslexic readers and non-dyslexic readers; no significant difference was found. Conclusion. This negative but important result, suggests no dysfunction of brainstem ocular motor circuits in dyslexic readers. It contrasts results on latencies related to visual attention dysfunction at cortical level.
To evaluate the effect of orthoptic treatment on the AC/A (A, accommodation; C, convergence) and CA/C ratios in subjects with convergence insufficiency (CI).
The change in AC/A and CA/C ratios after a 12-week period of home-based orthoptic treatment was examined in 10 subjects (mean age, 25.4+/-4.1 years [SD]). Both the AC/A and CA/C ratios were measured by using gradient response methods. For the AC/A ratio, the gradient phoria method was used, and for the CA/C ratio the prism-induced change in accommodation was measured with a refractometer.
No change in the AC/A and CA/C ratios (P>0.05) were found after orthoptic treatment. However, improvements were found (P<0.05) in the fast and slow vergence mechanisms.
Despite improvements in the fast and slow vergence mechanisms no change was found in the AC/A and CA/C ratios after orthoptic treatment in CI subjects. This finding is unexpected in light of the present understanding of CI, and an alternative theory is proposed.
There is a controversy as to whether dyslexic children present visuo-motor disabilities such as vergence and accommodative problems assessed with orthoptic tests. The purpose of this study is to re-examine this issue in a large population of children.
Extensive orthoptic evaluation was made in 57 dyslexic and 46 non-dyslexic ("normal") age-matched children. Convergence and divergence capacities were evaluated at two distances (30 cm and 400 cm).
Binocular vision measured with stereo-acuity tests was normal in dyslexics. In contrast, the near point of convergence was significantly more remote in dyslexics; most importantly, divergence at both far and near distance was significantly more reduced in dyslexics (median value 4 pD and 10 pD, respectively, at far and near) than in "normals" (median value 6 pD and 12 pD, at far and near).
The existence of the divergence deficit at far distance indicates the presence of deficit of divergence per se, independently from convergence and accommodation relaxation. This result is novel and corroborated by physiological studies indicating distinct control of convergence and divergence, both at the cortical and subcortical premotor level. We conclude that vergence deficits are frequently present in dyslexics, and that dyslexics should be re-educated; training should address distinctively convergence and divergence subsystems.
Background:
Prevalence of dyslexia is 5%-10% of the population. Opinions differ on how binocular function affects dyslexia. The aim of the present study was to evaluate the binocular function in dyslexic children and compare it with a group of age-matched control children.
Methods:
The study was performed at Ängkärrskolan and at Kungsholmen elementary schools in Stockholm, Sweden. Sixty-three children with dyslexia and 60 control children between fourth and ninth grade participated. Monocular and binocular visual acuity, refractive error, best corrected visual acuity at distance and near, near point of convergence, amplitude of accommodation, stereopsis, phorias, and fusional reserves were evaluated in all of the children.
Results:
The results show that there was no difference in the visual functions tested except for the amplitude of accommodation, which was found to be reduced both monocularly and binocularly in the dyslexic children.
Conclusion:
This study showed that only the amplitude of accommodation seems to differ in children with dyslexia as compared with the control children; however, the ability to accommodate was still good and is unlikely to hamper reading and learning ability. The results therefore support that the recent findings of binocular deficits in dyslexic children are a result of the phonological deficit of dyslexia and not an underlying cause of dyslexia.
Ss were 117 dyslexic children, constituting the total number of pupils from a school with specific remedial reading classes, and a comparable control series of 117 pupils from a normal school. The examinations performed showed that dyslexia is not due to refractive errors, impaired visual acuity, or orthoptic disorders. A doubtful preponderance was noticed of mild hypermetropia, slight astigmatism, and latent strabismus to near vision. Orthoptic treatment was indicated in 4% of these cases. There was a preponderance of crossed eye-hand dominance. It is concluded that word-blind children should be subjected to particular careful ophthalmological examination to prevent possibly existing visual anomalies from accentuating the true reading difficulties. No causal relation exists between specific dyslexia and visual defects in their widest sense. (16 ref.) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Abstract Eighty-six nine-year-old dyslexic children were matched to control children with regard to age, sex, class in school, and intelligence. Orthoptic and eye movement analysis were performed on all children. It was concluded that the dyslexic pupils did not differ significantly from control children in terms of strabismus, accommodation, stereo acuity, vergence function or ocular dominance. Eye movement recordings did not show any qualitative differences between the groups in vergence dynamics during synoptophore investigations.
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.
Learning disabilities constitute a diverse group of disorders in which children who generally possess at least average intelligence have problems processing information or generating output. Their etiologies are multifactorial and reflect genetic influences and dysfunction of brain systems. Reading disability, or dyslexia, is the most common learning disability. It is a receptive language-based learning disability that is characterized by difficulties with decoding, fluent word recognition, rapid automatic naming, and/or reading-comprehension skills. These difficulties typically result from a deficit in the phonologic component of language that makes it difficult to use the alphabetic code to decode the written word. Early recognition and referral to qualified professionals for evidence-based evaluations and treatments are necessary to achieve the best possible outcome. Because dyslexia is a language-based disorder, treatment should be directed at this etiology. Remedial programs should include specific instruction in decoding, fluency training, vocabulary, and comprehension. Most programs include daily intensive individualized instruction that explicitly teaches phonemic awareness and the application of phonics. Vision problems can interfere with the process of reading, but children with dyslexia or related learning disabilities have the same visual function and ocular health as children without such conditions. Currently, there is inadequate scientific evidence to support the view that subtle eye or visual problems cause or increase the severity of learning disabilities. Because they are difficult for the public to understand and for educators to treat, learning disabilities have spawned a wide variety of scientifically unsupported vision-based diagnostic and treatment procedures. Scientific evidence does not support the claims that visual training, muscle exercises, ocular pursuit-and-tracking exercises, behavioral/perceptual vision therapy, "training" glasses, prisms, and colored lenses and filters are effective direct or indirect treatments for learning disabilities. There is no valid evidence that children who participate in vision therapy are more responsive to educational instruction than children who do not participate.
We hypothesized that results of previous investigations indicating an increased prevalence of reading disability in boys compared with girls reflected a bias in subject selection. In an epidemiologic sample of 215 girls and 199 boys, we identified two groups of reading-disabled children: research identified and school identified. Results indicated no significant differences in the prevalence of reading disability in research-identified boys compared with research-identified girls in either second (17 [8.7%] of 196 boys; 15 [6.9%] of 216 girls) or third grade (18 [9.0%] of 199 boys; 13 [6.0%] of 215 girls). In contrast, school identification resulted in the classification of 27 (13.6%) of 198 boys and seven (3.2%) of 216 girls in second grade and 20 (10.0%) of 199 boys and nine (4.2%) of 215 girls in third grade. Our data indicate that school-identified samples are almost unavoidably subject to a referral bias and that reports of an increased prevalence of reading disability in boys may reflect this bias in ascertainment. These findings caution against relying solely on schools for identification of reading-disabled children.
(JAMA. 1990;264:998-1002)
This paper is a review of the literature relative to treatment results for convergence insufficiency utilizing vision therapy training procedures. Vision therapy is shown to improve the nearpoint of convergence and fusional convergence and to ameliorate associated symptoms. The overall cure rate is 72%. Furthermore, the training results appear to persist for at least 2 years if the patients are initially cured and are independent of age until the late presbyopic years. Also, recent studies indicate the type of training procedures which yield the most effective training results.
Seven patients with convergence insufficiency and related asthenopia underwent automated fusional convergence training. A matched-subjects control group crossover design was used to reduce placebo effects. All patients showed significant increases in vergence ranges with concurrent marked reduction of symptoms after training. All patients showed a flattening of and an increase in the base-out portion of their fixation disparity curve. Our results demonstrated the effectiveness of fusional vergence training in reducing asthenopia in these patients. Subsequent accommodation and vergence training using traditional orthoptic procedures yielded further reduction of asthenopia, as well as an increase in the base-out fusional range.
Visual therapy has long been considered an appropriate treatment for children with functional problems. The authors have expanded the parameters of effectiveness to include adults with convergence insufficiency.
Thirty-six children attending a private school for learning disabled children were diagnosed as having visual and/or perceptual disorders. The experimental group received individual programming in visual and perceptual development at their appropriate developmental levels. The control group received instruction in physical education, art or music classes. Both groups received individualized reading assistance. Statistical analysis of the two year demonstration project, which included nine months of actual training, indicated that the experimental group made significant gains in reading as compared to the control group. The improvement in basic instructional level of The Informal Reading Inventory (Temple University), and the Word Reading and Paragraph Meaning subtests of the Stanford Achievement Tests, and the actual classroom reading levels were all statistically significant. The Informal Word Recognition Inventory (Daniels) and the Spelling subtest of the Stanford Achievement Tests showed a definite trend approaching statistical significance.
Eighty-six nine-year-old dyslexic children were matched to control children with regard to age, sex, class in school, and intelligence. Orthoptic and eye movement analysis were performed on all children. It was concluded that the dyslexic pupils did not differ significantly from control children in terms of strabismus, accommodation, stereo acuity, vergence function or ocular dominance. Eye movement recordings did not show any qualitative differences between the groups in vergence dynamics during synoptophore investigations.
Eighty-six 9-year old dyslexic children were carefully matched to controls with regard to age, sex, class in school, and intelligence and thorough visual functions tests and eye examinations were performed. As a group the dyslexic pupils exhibited a lower distance as well as near visual acuity both with monocular and binocular viewing. Furthermore, the dyslexic pupils had a lower contrast sensitivity at the lower and higher spatial frequencies. These differences were all statistically significant. However, no statistically significant differences between the two groups could be observed regarding refractive errors or contrast sensitivity in the middle spatial frequency range. Although some eyes were amblyopic, any severe eye anomalies or diseases were not found in any of the investigated children.
The pattern of eye movements during reading was studied in 12 developmental dyslexics and in 10 age-matched controls. According to standard reading batteries, dyslexics showed marked reading slowness and prevalently used the sublexical procedure in reading. Eye movements were recorded while they read lists of short and long words or pseudowords. In normal readers, saccade amplitude increased with word length without a concomitant change in the number of saccades; in contrast, the number of saccades increased for long pseudowords. In dyslexics, the eye movement pattern was different. The number of saccades depended on stimulus length for both words and pseudowords while saccade amplitude remained small and constant. The sequential scanning shown by dyslexics for both words and pseudowords appears consistent with the cognitive description of the reading disorder which indicates the preferential use of the sublexical print-to-sound correspondence rules.
Supporting Children With Dyslexia: Practical Approaches for Teachers and Parents
- G Squires
- S Mckeown
Reading text increases binocular disparity in dyslexic children
- J A Kirby
- H I Blythe
- D Drieghe
- S P Liversedge
Visual therapy results for convergence insufficiency: A literature review
- J D Grisham
A randomized prospective masked and matched comparative study of orthoptic treatment versus conventional reading tutoring treatment for reading disabilities in 62 children
- D Atzmon
- P Nemet
- A Ishay
- E Karni
Everything You Need to Know About Dyslexia
- M Goldish
Vergence eye movements and dyslexia (Master's thesis)
- J K Green
- E Ullmark