Visual and Oculomotor Function in Developmental Dyslexia: A Systematic Review and Meta-Analysis.

This Issue At A Glance

The marked degree of heterogeneity in persons with developmental dyslexia has motivated the investigation of possible subtypes. Attempts have proceeded both from theoretical models of reading and the application of unsupervised learning (clustering) methods. Previous cluster analyses of data obtained from persons with reading disabilities have suffered from the inherent limitations of unsupervised learning methods. Specifically, the reliability and stability of cluster solutions have proven difficult to determine. Recent developments in the clustering literature have addressed these concerns by permitting checks on the internal validity of the solution. Resampling methods produce consistent groupings of the data independent of initialization effects, while the gap statistic provides a confidence measure for the determination of the optimal number of clusters present in the data. Combining these methods produces a robust data-driven classification that can be compared with theoretically based subtypes to produce better-informed models of developmental dyslexia. The present study is a novel application of resampling (bootstrap aggregating or bagging) methods and the gap statistic to the subtyping of children with developmental dyslexia. The specific aims of this study are: (1) to illustrate the use of bagging methods and the gap statistic in multivariate data obtained from children with developmental dyslexia; and (2) to compare the bagged clustering thresholded by the gap statistic against the predictions of the double-deficit hypothesis. The double-deficit hypothesis is a prominent theoretical model of developmental dyslexia, which predicts three subtypes: phonological, rate, and phonological-rate impaired readers. Three simulated data sets with known cluster structure were created to check the validity and illustrate the utility of the bagged clustering with the gap statistic in data with known structure. Subsequently, a clinical database of standardized test data (eight tests) from 93 children with developmental dyslexia was clustered using these methods. This procedure was repeated on a database of 93 children without reading disability matched for gender and age as a control. Finally, the clustering was repeated on the entire database of 186 participants. Cluster solutions were obtained for an increasing number of clusters (1-10) and were tested against the null hypothesis that no subtypes were present, i.e. the data represented a single cluster. Four clusters were identified in the children with developmental dyslexia. There was no evidence of significant cluster structure in the children without dyslexia. Two clusters were identified when children with and without reading impairments were considered together. Among the participants with developmental dyslexia, there was evidence of a phonological-deficit cluster, a rapid-naming cluster, and a cluster showing both depressed phonological processing and rapid naming. These accounted for 73 of the 93 participants (78%). All three are predicted by the double-deficit hypothesis. The fourth cluster consisted of children with normal phonological and rapid naming ability incommensurate with their high verbal ability. An analysis of variance with post-hoc multiple comparisons demonstrated that the phonological, rapid-naming, and double deficit clusters did not differ significantly in age, but the fourth cluster was comprised of significantly older children. The mixed data set revealed two clusters. One cluster consisted almost entirely of the double-deficit and phonological subtypes. The other consisted of the participants without dyslexia and the children with dyslexia demonstrating either a single rapid naming deficit or standardized test scores in the normal range. A silhouette analysis indicated that the four-cluster solution for the children with developmental dyslexia was superior to the two-cluster solution obtained for the entire data set. The study provides support for the presence of distinct subtypes in children with developmental dyslexia and for the double-deficit hypothesis. Specifically, this study finds three subtypes predicted by the double-deficit hypothesis without the assumption of an a priori theoretical model of reading. Taken together, these subtypes account for 79% of the participants with dyslexia. Further, the percentages of children in each subtype are in good agreement with previous studies. The participants in the subtype not predicted by the double-deficit hypothesis were significantly older than the other three groups. Recent advances in unsupervised learning can be expected to aid the improvement and refinement of the definition of developmental dyslexia. If reliable and consistent subtypes can be identified among persons with developmental dyslexia, it is reasonable to assume that diagnostic and intervention efforts will be greatly improved.

Introduction: Acute acquired comitant esotropia (AACE) is a rare type of esotropia for which until now the main treatment modalities prescribed are prism glasses, botulinum toxin injection and surgery. The purpose of our study is to compare the surgical outcomes in patients with AACE managed with and without pre-operative prism adaptation test (PAT). Methods: We have done a prospective, interventional study for the duration of one year. Forty patients with AACE were randomly divided into two groups by computerized randomization – those undergoing surgery after pre- operative PAT and those undergoing surgery without it. In control group (Group C), patients underwent surgery based on the angle of deviation at distance measured by prism bar cover test (PBCT) and wearing full cycloplegic correction, while in test group (Group T), patients underwent surgery based on the preoperative prism-adapted angle at distance wearing prism power determined by PBCT and wearing full cycloplegic correction. The primary outcome was post-operative deviation and secondary outcome was stereopsis. Post-operatively, patients were followed up at week 1, week 4 and final follow-up was done at week 12. Results: The mean age of the 40 patients was 13.95 ± 5.36 years. The age of the youngest and the oldest patients enrolled were 8 years and 35 years, respectively. The mean SD (standard deviation) of the PBCT for distance (measured in prism diopters – PD), PBCT for near (measured in prism diopters – PD) and stereopsis for near (measured in seconds of arc using Titmus Fly Test) at last follow-up visit (week 12) in the test versus control group were as follows: 1.70 ± 1.42 PD versus 4.75 ± 3.39 PD, 2.55 ± 1.82 PD versus 6.95 ± 3.35 PD and 74.90 ± 53.47 sec of arc versus 48.60 ± 31.97 sec of arc, respectively, which were statistically significant (p = <0.01, p = <0.01 and p = .03, respectively). The change in visual acuity and spherical equivalent in each group was insignificant. Discussion: Surgical outcomes in patients of AACE are better when surgical planning is done after performing pre-operative PAT as opposed to when surgery is planned without PAT. Better motor alignment (less under correction and over correction) and better sensory results in terms of improvement in stereopsis were observed. We recommend the use of pre-operative PAT in surgical planning in patients of AACE.

Extensive research has shown that phonological awareness including phoneme awareness skills are vital when children acquire literacy skills in alphabetic languages especially in English. Furthermore, research on developmental dyslexia (DD) especially in English has been conducted with research-informed/well-established definitions of DD. This is because compared to other languages, the prevalence of DD in English is high, and thus children with DD form a large minority group. These dyslexia research encompasses cognitive-behavioural, neuroimaging, behavioural and molecular-genetic studies. There seems to be a consensus amongst these researchers that DD manifests itself as a phonological deficit, and thus the phonological deficit hypothesis (as well as naming disfluency) for DD has become prominent in the alphabetic languages, especially in English. This is because print-to-sound or sound-to-print mappings in English are not always one-to-one and thus opaque/inconsistent. Now important questions arise in discussing how children acquire reading skills in non-alphabetic languages especially in Japanese where logographic Kanji and 2-forms of syllabic Kana are used: (i) are phonological awareness skills vital when children learn to read in Japanese? (ii) can the phonological deficit hypothesis explain DD in Japanese? These questions will be addressed in this paper by comparing the behavioural and some neuroimaging studies in alphabetic languages and Japanese Kanji and Kana as well as Chinese, another non-alphabetic languag. It seems that phonological awareness may not be as important for non-alphabetic languages such as Chinese or Japanese at the start of literacy acquisition. Phonological awareness become important skills in Chinese and Japanese only when children are older. Instead of phonological awareness other metalinguistic awareness skills are important for acquisition of reading in Chinese and Japanese such as orthographic or morphological awareness (Chinese), vocabulary size (Japanese), visuo-spatial processing (Chinese and Japanese) and visual-motor integration (Chinese and Japanese) skills. Also available neuroimaging studies will be used to uncover the behavioural dissociation and the neural unity in an English-Japanese bilingual adolescent boy with monolingual dyslexia in English.

Objective Many studies report a deficit in working memory in children with Developmental Dyslexia (DD) and Developmental Coordination Disorder (DCD) compared to children with Typical Development (TD). In this study, we questioned the working memory profile of children with co-occurring Developmental Dyslexia and Developmental Coordination Disorder (DD-DCD). First, we hypothesized that children with DD would have a more substantial deficit in verbal working memory, while children with DCD would have a more substantial deficit in visuospatial working memory. For the comorbid group, we postulated a deficit in both the verbal and visuospatial domains. Second, we determined whether we could correctly distinguish between the four groups based on their working memory profiles. Method 47 children with DD, 22 children with DCD, 27 children with DD-DCD, and 42 TD children aged from 7.6 to 12.6 years were tested on the phonological loop, the visuospatial sketchpad, and the central executive using the Digit Span and Wechsler’s Block-tapping tests. Results Children with DD had a deficit in verbal working memory including a specific deficit in the phonological loop and children with DCD had a deficit in visuospatial working memory. Comorbid children had poorer performance in verbal working memory (like group with DD) and in visuospatial working memory (like group with DCD). Exploratory cluster analysis resulted in four subgroups: (1) one cluster with good working memory performance made up of most of the TD children; (2) one cluster with a phonological loop deficit mainly made up of the children with DD; (3) one cluster with poor visuospatial working memory capacities mostly made up of the children with DCD (± DD) and (4) one cluster with average performance made up of children from all the groups. Conclusion Our results underline the importance of taking comorbidity into account when testing working memory in children with learning disabilities.

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ABSTRACTRecent work exploring syntax in developmental dyslexia (DD) has identified morphosyntactic deficits, striking parallelisms between children with DD and specific language impairment (SLI). The question remains open if the underlying causes for such deficits are related to difficulties in phonology, which is affected in DD, or to working memory, as has been previously reported for SLI. We focus on the production of third person accusative clitic pronouns (ACC3) and of homophonous definite determiners in French-speaking children with DD and SLI as well as typically developing (TD) controls. If syntactic complexity modulates performance of DD children, as has already been shown for SLI, we predict children with DD to perform significantly worse on ACC3 compared to definite determiners, which are homophonous but syntactically simpler. In addition, if impairment in ACC3 stems from phonology or working memory difficulties, we expect ACC3 performance in both clinical groups to relate to performance on non-word repetition or forward/backward digit spans. We studied 2 groups of 21 children and adolescents, with DD and SLI (7–15 years) and age-matched TD controls. Results reveal significant weaknesses with ACC3 in DD and SLI groups compared to TD controls, but no difficulty for homophonous definite determiners, confirming a deficit relating specifically to syntactic complexity. As for links to phonology and working memory, a single correlation emerged between ACC3 and the backward digit span in SLI, but not in DD, suggesting different underlying sources for syntactic deficits in these populations. Clinical implications of these results are discussed.

The purpose of this study was to examine whether developmental dyslexia (DD) is characterized by deficiencies in speech sensory and motor feedforward and feedback mechanisms, which are involved in the modulation of phonological representations. A total of 42 adult native speakers of Dutch (22 adults with DD; 20 participants who were typically reading controls) were asked to produce /bep/ while the first formant (F1) of the /e/ was not altered (baseline), increased (ramp), held at maximal perturbation (hold), and not altered again (after-effect). The F1 of the produced utterance was measured for each trial and used for statistical analyses. The measured F1s produced during each phase were entered in a linear mixed-effects model. Participants with DD adapted more strongly during the ramp phase and returned to baseline to a lesser extent when feedback was back to normal (after-effect phase) when compared with the typically reading group. In this study, a faster deviation from baseline during the ramp phase, a stronger adaptation response during the hold phase, and a slower return to baseline during the after-effect phase were associated with poorer reading and phonological abilities. The data of the current study are consistent with the notion that the phonological deficit in DD is associated with a weaker sensorimotor magnet for phonological representations.

BackgroundCerebral Visual Impairment (CVI) is a very common finding in children affected by Cerebral Palsy (CP). In this paper we studied the characteristics of CVI of a large group of children with CP and CVI, describing their neurovisual profiles according to three different age subgroups (subgroup 1: infants 6 months–2 years; subgroup 2: pre-school age 3–5 years; subgroup 3: school age ≥ 6 years).MethodsWe enrolled 180 subjects (104 males, mean age 66 ± 42.6 months; range 6–192 months) with CP and CVI for the study. We carried out a demographic and clinical data collection, neurological examination, developmental or cognitive assessment, and a video-recorded visual function assessment including an evaluation of ophthalmological characteristics, oculomotor functions, and basic visual functions. In school-aged children, we also performed an evaluation of their cognitive-visual profiles.ResultsThere were signs of CVI in all the three subgroups. Subgroup 1 (62 children) and subgroup 2 (50 children) were different for fixation (p = 0.02), visual acuity (p = 0.03) and contrast sensitivity (p < 0.01), being more frequently impaired in younger children. Comparing subgroup 2 with subgroup 3 (68 children), the older children presented more frequently myopia (p = 0.02) while the younger ones esotropia (p = 0.02) and alteration in smooth pursuit (p = 0.03) and saccades (p < 0.01). Furthermore, fixation, smooth pursuit, visual acuity, contrast sensitivity and visual filed (p < 0.01) were more frequently impaired in younger children (subgroup 1) compared to the older ones. Multiple correspondence analysis (MCA) confirmed the different neurovisual profiles according to age: younger children with CP showed more signs of CVI compared to the older ones. 34 out of 68 children belonging to subgroup 3 underwent the cognitive visual evaluation; an impairment of cognitive visual skills was detected in 21 subjects.ConclusionYounger children with CP showed more signs of CVI compared to the older ones, likely for the physiological maturation of visual system and mechanisms of neuroplasticity. In this direction, we suggest an early neurovisual evaluation to detect any weak visual functions.

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P17. Impaired auditory attention in adolescents with developmental dyslexia

The purpose of this study was to document the effects of positive fusional vergence therapy and to determine the most effective timing of such training. Four experimental protocols were selected and five subjects were assigned randomly to each of the four experimental groups. Each subject in each group spent 120 min (total) over a period of 3 weeks doing positive fusional vergence training. Group A trained in twelve 10‐min sessions; group B in six 20‐min sessions; and group C in three 40‐min sessions. Group D was a control group. All the training was in‐office and consisted of positive fusional vergence training on the synoptophore. Each of the test groups showed increases in their positive fusional vergence ability at both distance and near. Group A (shorter sessions) demonstrated the largest increases overall. In addition, the group which trained in short 10‐min sessions (Group A) was the only one which showed significant increases in the negative fusional vergences and the positive blur finding. I conclude that it is best to use short, frequent training sessions to increase the amplitude of positive fusional vergence. The results and implications of the study are discussed briefly.

Recent research with English developmental dyslexics comparing the picture naming performance of these children to the picture naming performance of non-dyslexic (‘garden variety’) poor readers, reading age matched controls and chronological age matched controls has suggested that a selective difficulty in retrieving the phonological codes of known names on demand underlies the picture naming deficit found in developmental dyslexia (Swan & Goswami, Picture naming deficits in developmental dyslexia: the phonological representations hypothesis, Brain and Language, 56 (1997), 334–353). If the underlying causal factors in dyslexia are independent of the orthography that the child is learning to read, then a difficulty in retrieving the phonological codes of known names on demand should also be found in developmental dyslexics who are learning to read other languages. We therefore set out to replicate Swan and Goswami’s study with a group of German developmental dyslexics. We were interested to see whether a phonological deficit is characteristic of dyslexia in all orthographies, even those, such as German, in which high orthographic transparency means that dyslexic children read with considerable accuracy.

Due to the fact that it is frequently difficult to identify their etiological origins, reading and writing difficulties have inconsistent terminology in the literature. This article is a review and attempts to initiate a discussion about visual dyslexia. The authors pose the question whether - in the context of new neuroimaging methods and the neurosciences broadly defined - there exist reading and writing difficulties that stem from impaired functioning of the visual system and whether they can be assigned to developmental dyslexia. If it is assumed that developmental dyslexia is linguistic in nature, these are phonological deficits that come to the fore in children entering the world of reading. These phonological processing deficits impair word decoding (word identification), making word recognition impossible, thus preventing access to higher-order linguistic processes, that is comprehending meaning from texts or building one’s own narratives.

ABSTRACTPurpose: To study binocular and accommodative characteristics and their associations with age and gender in an Iranian young adult population.Methods: In this cross-sectional study, multistage cluster sampling was done from the students of Mashhad University of Medical Sciences. All participants had visual acuity, refraction, and cover tests followed by measurements of the near point of convergence (NPC), amplitude of accommodation (AA), monocular and binocular accommodative facility (MAF and BAF) using ±2.00 diopter (D) flipper lenses, and negative and positive relative accommodation (NRA and PRA). Near and distance fusional vergence reserves were measured using prism bar, and near associated phoria was assessed using the Mallett unit.Results: The mean age of the participants was 22.5±4.4 years (range: 18-35 years). The binocular and accommodative characteristics and their means in the studied sample included: mean distance dissociated phoria: 1.15 exophoria±2.04 prism diopters (PD), near dissociated phoria: 5.02 exophoria±4.74 PD, near associated phoria: 0.55 base-in±1.02, gradient accommodative convergence/accommodation (AC/A) ratio: 4.66±1.59, NPC: 5.27±3.60 cm, MAF: 11.33±5.58 cpm, BAF: 8.84±4.47 cpm, NRA: 2.08±0.33 D, PRA:-2.92±0.76 D, and AA: 11.14±2.6 D. In the multiple regression model including age and gender, near exophoria was significantly higher in men and levels of near base-out-break and near base-out-recovery were higher in females. Distance exophoria, distance base-in-break, distance base-in-recovery, and NPC increased with age and near base-out-break, PRA, BAF, MAF, and AA significantly decreased with age.Conclusion: Studied indices in this study significantly differ from available guidelines and these differences must be considered when making diagnostic or therapeutic decisions. Certain indices can be affected by age and gender.