Spherical lenses and prisms lead to postural instability in both dyslexic and non dyslexic adolescents

Phoneme Representation and Articulatory Impairment: Insights from Adults with Comorbid Motor Coordination Disorder and Dyslexia

Phonemic processing skills are impaired both in children and adults with dyslexia. Since phoneme representation development is based on articulatory gestures, it is likely that these gestures influence oral reading-related skills as assessed through phonemic awareness tasks. In our study, fifty-two young dyslexic adults, with and without motor impairment, and fifty-nine skilled readers performed reading, phonemic awareness, and articulatory tasks. The two dyslexic groups exhibited slower articulatory rates than skilled readers and the comorbid dyslexic group presenting with an additional difficulty in respiratory control (reduced speech proportion and increased pause duration). Two versions of the phoneme awareness task (PAT) with pseudoword strings were administered: a classical version under time pressure and a delayed version in which access to phonemic representations and articulatory programs was facilitated. The two groups with dyslexia were outperformed by the control group in both versions. Although the two groups with dyslexia performed equally well on the classical PAT, the comorbid group performed significantly less efficiently on the delayed PAT, suggesting an additional contribution of articulatory impairment in the task for this group. Overall, our results suggest that impaired phoneme representations in dyslexia may be explained, at least partially, by articulatory deficits affecting access to them.

Disconjugate Eye Movements in Dyslexic Adolescents While Viewing Op Art: A Creative Handicap?

Op art was created, in part, to produce illusions of movement. Given that dyslexics have been shown to have impaired visuo-postural axis deficits, it may be possible that dyslexics see illusions different than their non-dyslexic peers. To test this theory, we measured eye movement and posture in 47 dyslexic (18 female, 29 male; mean age 15.4) and 44 non dyslexic (22 female, 22 male; mean age 14.8) adolescents while they viewed three works of art by Op artist Bridget Riley. They then responded to a questionnaire about how they felt while viewing the artworks. Dyslexics demonstrated significantly slower saccades in terms of average velocity that was particularly disturbed in paintings that manipulated depth. Subjectively, dyslexics felt much more destabilized compared to their peers; however, there was not a significant difference in objective postural measurements between the two groups. The sensation of destabilization was positively correlated with appreciation in non-dyslexic adolescents. These subjective results suggest that dyslexics may be more sensitive to movement in depth, which could be related to the instability in vergence movements. Whereas this instability represents a hinderance in relation to reading, it could be an advantage while viewing paintings such as these.

Effects of Prismatic Lenses on Lateral Axial Dystonia in Parkinson's Disease: A Pilot Study

OBJECTIVE: In Parkinson's disease (PD), postural abnormalities such as lateral axial dystonia (LAD) are relatively common. Evidence suggests that both peripheral and central mechanisms contribute to these postural abnormalities. We previously reported an improvement in LAD following the use of prisms in two PD patients. Here, we further investigate the effects of prismatic lenses in a case series of nine patients with PD and LAD. METHODS: Nine patients underwent an orthoptic evaluation and were provided with prismatic lenses. Patients were evaluated at baseline and after one and three months of permanent prismatic lens use and again re-evaluated one month after the discontinuation of prismatic lens use. RESULTS: We found a linear relationship between disease duration and LAD severity. Compared to basal measurements, we observed a slight improvement in LAD. Furthermore, we found a significant reduction in self-perceived back pain due to the use of prismatic lenses. There was no significant association between the individual effects of prismatic lenses in patients with PD and their baseline LAD or other clinical and demographic features (all P>0.05). CONCLUSION: The present pilot study provides novel data on the possible effectiveness of prismatic lenses for LAD treatment in PD patients.

Visual, musculoskeletal and balance symptoms in individuals with visual impairment

BACKGROUND

Visual impairment is globally among the most prevalent disabilities. Research concerning the health consequences of visual deficits is challenged by confounding effects of age, because visual impairment becomes more prevalent with age. This study investigates the influence of visual deficits on visual, musculoskeletal and balance symptoms in adults with and without visual impairment, while controlling for age effects.

METHODS

Thirty-nine patients with visual impairment, aged 18-72 years, were compared to 37 age-matched controls with normal vision, allocated to two age groups: < 45 and ≥ 45 years. Self-reported symptoms were measured using the Visual, Musculoskeletal and Balance Symptoms Questionnaire and compared with demographic and optometric variables.

RESULTS

In total, patients with visual impairment reported more symptoms than age-matched normally sighted controls. Younger adults in the control group were almost free from symptoms, whereas younger adults with visual impairment reported levels of symptoms equal to older adults with visual impairment. Multiple logistic regression modelling identified use of eyeglasses, magnifying aids and presence of anisometropia to be the most influential risk factors for reporting visual, musculoskeletal and balance symptoms, with accentuated influence on balance symptoms.

CONCLUSIONS

People with visual impairments and people with age-related normal visual deficits are both predisposed to report visual, musculoskeletal and balance symptoms relative to people without visual defects or need for eye-wear correction. Age-related variations in symptoms were observed in the control groups but not in the visual impairment groups, with younger visual impairment patients reporting as many symptoms as older visual impairment patients. These findings indicate a need for a wider interdisciplinary perspective on eye care concerning people with visual impairment and people with need for habitual daily use of eye wear correction.

Reeducation of vergence dynamics improves postural control

INTRODUCTION

The purpose was to investigate the effect of vergence reeducation on postural control, in subjects with isolated vergence disorders.

MATERIAL AND METHODS

We studied the dynamics of vergence in 19 subjects (20-44 years old) using video-oculography (Eye See Cam). On the basis of orthoptic and symptomatology assessments, ten of the subjects were diagnosed for vergence disorders then vergence eye movements were reeducated with the REMOBI method (US8851669, 5 weekly sessions lasting for 35min). Postural control was measured before and after reeducation, postural recording was done in upright stance (Dynaport), with both eyes closed or open and looking a visual target located at 2m distance.

RESULTS

After reeducation with REMOBI, the visual symptomatology faded away and the stereoacuity improved at least for some subjects; the vergence latency decreased significantly and the vergence accuracy increased significantly. In terms of posture, the Mean Power Frequency (MPF) of the body sway decreased significantly in both eyes open and eyes closed conditions. Considering all subjects together (i.e. healthy subjects and subjects with vergence disorders before the reeducation), the antero-posterior body sway (Root Mean Square A/P) was positively correlated with the visual symptomatology: the higher the visual symptomatology, the higher was the body sway.

CONCLUSION

The results bring evidence for synergy between the quality of vergence and the quality of postural control. They open a new research line that bridges the gap between neuroscience, ophthalmology-orthoptics and posturology.

The distinctive vertical heterophoria of dyslexics

In this study, we looked for the presence of vertical heterophoria (VH) in 42 dyslexic children (22 males and 20 females) aged 118.5±12.9 months who were compared with a control group of 22 nondyslexic children (eleven males and eleven females) aged 112±9.8 months. Dyslexics presented a low-level (always <1 prism diopter) VH combined with torsion. This oculomotor feature clearly separates the dyslexic group from the normal readers group. It is independent of the type of dyslexia. The essential feature of this VH is a lability that appears during specific stimulation of sensory receptors involved in postural regulation. This lability is demonstrated using a vertical Maddox test conducted under very specific conditions in which postural sensors are successively stimulated in a predetermined order. A quantitative variation in this VH may be seen during the Bielchowsky Head Tilt Test, which reveals hypertonia of the lower or upper oblique muscles. Vertical orthophoria can be achieved by placing low-power prisms asymmetrically within the direction of action of the superior or inferior oblique muscles. The selection of power and axis is not only guided by elements of the eye examination but also from observation of postural muscle tone. All these elements suggest that the VH could be of postural origin and somehow related to the vertical action of the oblique muscles. VH and torsion are not harmful per se. There is no statistical relationship between their level and the various parameters used to assess the reading skills of dyslexic children. VH and torsion could be a clinical marker of global proprioceptive dysfunction responsible for high-level multisensory disturbances secondary to poor spatial localization of visual and auditory information. This dysfunction might also explain the motor disorders concomitant to dyslexia.

Temporal Co-Variation between Eye Lens Accommodation and Trapezius Muscle Activity during a Dynamic Near-Far Visual Task

Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy controls and 12 patients with a history of visual and neck/shoulder symptoms performed a Near-Far visual task under three different viewing conditions; one neutral condition with no trial lenses, one condition with negative trial lenses to create increased accommodation, and one condition with positive trial lenses to create decreased accommodation. Eye lens accommodation and trapezius muscle activity were continuously recorded. The trapezius muscle activity was significantly higher during Near than during Far focusing periods for both groups within the neutral viewing condition, and there was a significant co-variation in time between accommodation and trapezius muscle activity within the neutral and positive viewing conditions for the control group. In conclusion, these results reveal a connection between Near focusing and increased muscle activity during dynamic changes in focus between a nearby and a far target. A direct link, from the accommodation/vergence system to the trapezius muscles cannot be ruled out, but the connection may also be explained by an increased need for eye-neck (head) stabilization when focusing on a nearby target as compared to a more distant target.