Contrast sensitivity in infants and children with Down syndrome

Neuro-Ophthalmological Manifestations in Children with Down Syndrome: Current Perspectives

Down syndrome, caused by an extra copy of all or part of chromosome 21, is the most prevalent intellectual disability of genetic origin. Among numerous comorbidities which are part of the phenotype of individuals with Down syndrome, ocular problems appear to be highly prevalent. Neuro-ophthalmological manifestations, such as ocular alignment and motility disturbances, amblyopia, hypoaccommodation or optic nerve abnormalities, and other organic ocular anomalies frequently reported in Down syndrome, may lead to an overall decrease in visual acuity. Although numerous studies have reported ocular anomalies related to Down syndrome, it remains challenging to determine the impact of each anomaly upon the decreased visual acuity, as most such individuals have more than one ocular problem. Even in children with Down syndrome and no apparent ocular defect, visual acuity has been found to be reduced compared with typically developing children. Pediatric ophthalmological examination is a critical component of a multidisciplinary approach to prevent and treat ocular complications and improve the visual outcome in children with Down syndrome. This narrative review aims to provide a better understanding of the neuro-ophthalmological manifestations and discuss the current ophthalmological management in children with Down syndrome.

Bifocals reduce strabismus in children with Down syndrome: Evidence from a randomized controlled trial

PURPOSE

Children with Down syndrome (DS) more often have strabismus, refractive errors, accommodative lags and reduced visual acuity (VA) than typically developing children. In this study, we compare the effects of bifocal glasses with those of unifocal glasses in children with DS. Changes in angle of strabismus, accommodation and refractive error were analysed in this paper.

METHODS

In a multicentre randomized controlled trial, 119 children with DS, aged 2-16, were randomly allocated for bifocal or unifocal glasses (with full correction of refractive error in cycloplegia). The 15 centres, all in the Netherlands, followed the participants for 1 year. Changes in refractive error, accommodative accuracy, strabismus, binocularity and stereopsis were compared across 4 subsequent visits.

RESULTS

Refractive errors and accommodative errors showed no significant change throughout the course of our study in either intervention group. The manifest angle of strabismus, however, reduced significantly in the bifocal group. This improvement was observed shortly after the children received their new correction (~6 weeks) (linear regression: t = 3.652, p < 0.001) and remained present in the final measurements after 1 year (linear regression: t = 3.604, p < 0.001). The percentage of children with positive binocularity and stereo tests showed no significant differences between the groups.

CONCLUSION

Bifocals with full correction of refractive error reduce the manifest angle of strabismus within a few weeks. No effects on accommodation, refractive error, stereopsis and binocularity occurred over the course of 1 year.

Abnormalities of the Optic Nerve in Down Syndrome and Associations With Visual Acuity

Background: Various ocular anomalies are present in the vast majority of individuals with Down syndrome; however, we know little about optic nerve abnormalities. The aim of this cross-sectional comparative study was to describe optic disc morphology in patients with Down syndrome and to determine if the differences found are potentially related to visual acuity.

Subjects/methods: Assessable fundus images were obtained in 50 children with Down syndrome and 52 children without Down syndrome. Morphological analysis of the optic nerve was performed, including the disc-to-macula distance (DM) to disc diameter (DD) ratio (DM/DD), the cup-to-disc ratio and optic disc ovality. Data relating to ophthalmological status were retrospectively analyzed to evaluate the possible causes of reduced visual acuity.

Results: DM/DD was significantly larger (p = 0.0036) and the cup-to-disc ratio was significantly smaller (p = 0.018) in children with Down syndrome, compared to controls. The optic discs were also more frequently torted (p = 0.034), tilted (p = 0.0049) and oval (p = 0.026). Furthermore, crescents (p = 0.0002), peripapillary atrophy (p = 0.0009), and pigment anomalies (p < 0.0001) were also more prevalent in children with Down syndrome than in those without. Visual acuity was significantly lower in children with Down syndrome compared to controls with similar refraction problems and strabismus prevalence (p < 0.0001). The mean DM/DD and the presence of a crescent was not directly related to visual acuity (r = 0.39, p = 0.31), (r = 0.35, p = 0.12) respectively. Visual acuity was diminished in 80% of children with Down syndrome and the smallest discs and in 84% of those with tilted discs. However, other causes may contribute to the diminished visual acuity in these cases.

Conclusion: The optic nerve head in children with Down syndrome is affected by various anatomical and developmental abnormalities. Unrelated to refraction (spherical equivalent), the optic discs appear smaller and more frequently mal-inserted in Down syndrome. Optic disc hypoplasia, as well as severe tilting, may reduce vision but they do not represent major contributors to the decrease of vision in such children. As these children often have multiple ocular and neurosensory problems, it remains challenging to relate visual acuity problems with a specific abnormality. Smaller discs may lead to optic disc drusen formation in children with Down syndrome.

Effects of bifocals on visual acuity in children with Down syndrome: a randomized controlled trial

Purpose

Children with Down syndrome (DS) typically have reduced visual acuity (VA) and accommodation lag, but it is unclear whether prescribed glasses should correct both distance VA (DVA) and near VA (NVA) due to the lack of RCTs. We therefore conducted a multicentre RCT to compare the effects of bifocals designed to correct both DVA and NVA with distance‐correcting unifocal glasses in children with DS.

Methods

A total of 119 children with DS, aged 2–16, were randomly allocated for bifocal or unifocal glasses (with full correction of refraction error in cycloplegia) in 14 Dutch hospitals and followed during 1 year. VA data were analysed in relation to baseline VA with ancova.

Results

Treatment groups showed no differences at baseline. Shortly after receiving new corrections (~6 weeks), uncrowded NVA (bifocals 0.18 ± 0.33 LogMar; unifocals 0.09 ± 0.19 LogMar) and crowded NVA with bifocals (bifocals 0.13 ± 0.36 LogMar; unifocals 0.08 ± 0.33 LogMar) were significantly better than at baseline, but these short‐term improvements in NVA were not significantly different between the two treatments (p > 0.151). The 1‐year treatment differences were as follows: significantly larger improvement for bifocals compared to unifocals in both uncrowded NVA (bifocals 0.23 ± 0.29 LogMar, unifocals 0.12 ± 0.30 LogMar, p = 0.045) and crowded NVA (bifocals 0.31 ± 0.28 LogMar; unifocals 0.16 ± 0.30 LogMar, p = 0.017). Improvements in DVA were comparable (bifocals 0.07 ± 0.21 LogMar, unifocals 0.08 ± 0.22 LogMar, p = 0.565). Children with poor baseline VA improved more. Accommodation lag stayed unchanged.

Conclusion

After one year, bifocals with full correction of ametropia led to significantly larger improvement of both uncrowded NVA and crowded NVA in children with DS with accommodation lag compared to unifocals.

Image Quality Metric Derived Refractions Predicted to Improve Visual Acuity Beyond Habitual Refraction for Patients With Down Syndrome

Purpose

To determine which optimized image quality metric (IQM) refractions provide the best predicted visual acuity (VA).

Methods

Autorefraction (AR), habitual refraction (spectacles, n = 23; unaided, n = 7), and dilated wavefront error (WFE) were obtained from 30 subjects with Down syndrome (DS; mean age, 30 years; range, 18–50). For each eye, the resultant metric value for 16 IQMs was calculated after >25000 sphero-cylindrical combinations of refraction were added to the measured WFE to generate residual WFE. The single refraction corresponding to each of the 16 optimized IQMs per eye was selected and used to generate acuity charts. Charts also were created for AR, habitual refraction, and a theoretical zeroing of all lower-order aberrations, and grouped into 10 sets with a clear chart in each set. Dilated controls (five observers per set) read each chart until five letters were missed on a high contrast monitor through a unit magnification telescope with a 3 mm pupil aperture. Average letters lost for the five observers for each chart was used to rank the IQMs for each DS eye.

Results

Average acuity for the best performing refraction for all DS eyes was within five letters (0.11 ± 0.05 logMAR) of the clear chart acuity. Optimized IQM refractions had ∼3.5 lines mean improvement from the habitual refraction (0.37 ± 0.22 logMAR, P < 0.001). Three metrics (Visual Strehl Ratio [VSX], VSX computed in frequency domain [VSMTF], and standard deviation of intensity values [STD]) identified refractions that were ranked first, or within 0.09 logMAR of first, in >98% of the eyes.

Conclusions

Optimized IQM refraction is predicted to improve VA in DS eyes based on control observers reading simulated charts.

Translational Relevance

Refractions identified through optimization of IQM may bypass some of the challenges of current refraction techniques for patients with DS. The optimized refractions are predicted to provide better VA compared to their habitual correction.

Different visual development: norms for visual acuity in children with Down's syndrome

BACKGROUND

Visual acuity is known to be poorer in children with Down's syndrome than in age-matched controls. However, to date, clinicians do not have access to norms for children with Down's syndrome that allow differential discrimination of healthy from anomalous visual development in this population.

METHODS

The Down's Syndrome Vision Research Unit at Cardiff University has been monitoring visual development in a large cohort of children since 1992. Cross-sectional data on binocular visual acuity were retrospectively analysed for 159 children up to 12 years of age in order to establish binocular acuity norms. Longitudinal binocular acuity data were available for nine children who were seen regularly over the 12 years age-range. Monocular acuity was successfully recorded less often in the cohort, but analysis of scores for 69 children allowed assessment of inter-ocular acuity differences and binocular summation.

RESULTS

In comparison with published norms for the various acuity tests used, binocular acuity was consistently poorer in children with Down's syndrome from the age of three years and stabilised at around 0.25 logMAR from the age of four years. Inter-ocular acuity difference and binocular summation were both 0.06 logMAR, which is similar to the reported values in children without Down's syndrome.

CONCLUSIONS

The study provides eye-care practitioners with the expected values for binocular acuity in children with Down's syndrome and demonstrates the visual disadvantage that children with Down's syndrome have when compared with their typically developing peers. The results emphasise the responsibility that practitioners have to notify parents and educators of the relatively poor vision of children with Down's syndrome, and the need for classroom modifications.

Visual characteristics of children with Down syndrome

PURPOSE

To analyze long-term visual development in children with Down syndrome who received early ophthalmological intervention.

METHODS

A total of 125 children with Down syndrome who were examined before 6 years of age and followed up for more than 5 years were selected. Visual development, refraction, visual acuity testing, and the prescription of spectacles were examined retrospectively.

RESULTS

Mean visual acuity by age was as follows: 2 years, 1.13 ± 0.23 logarithm of the minimum angle of resolution (logMAR); 5 years, 0.55 ± 0.25 logMAR; 8 years, 0.27 ± 0.19 logMAR; 11 years, 0.17 ± 0.16 logMAR; and 14 years, 0.10 ± 0.15 logMAR. In 32 children (25.6%), visual acuity reached 0.0 logMAR or better. Hyperopia of +2D or more was observed in 132 eyes (52.8%), and astigmatism of 2D or more was observed in 153 eyes (61.2%). Subjective testing was difficult in many children prior to 4.5 years of age, and grating acuity testing was necessary. Spectacles were prescribed at a mean age of 3.5 ± 1.6 years in 120 children (96.0%). The average duration until the spectacles were worn constantly was 9.0 ± 9.3 months.

CONCLUSION

Early ophthalmological intervention and longitudinal care is important for children with Down syndrome.

Early environmental therapy rescues brain development in a mouse model of Down syndrome

Down syndrome (DS), the most common genetic disorder associated with intellectual disabilities, is an untreatable condition characterized by a number of developmental defects and permanent deficits in the adulthood. Ts65Dn mice, the major animal model for DS, display severe cognitive and synaptic plasticity defects closely resembling the human phenotype. Here, we employed a multidisciplinary approach to investigate, for the first time in developing Ts65Dn mice, the effects elicited by early environmental enrichment (EE) on brain maturation and function. We report that exposure to EE resulted in a robust increase in maternal care levels displayed by Ts65Dn mothers and led to a normalization of declarative memory abilities and hippocampal plasticity in trisomic offspring. The positive effects of EE on Ts65Dn phenotype were not limited to the cognitive domain, but also included a rescue of visual system maturation. The beneficial EE effects were accompanied by increased BDNF and correction of over-expression of the GABA vesicular transporter vGAT. These findings highlight the beneficial impact of early environmental stimuli and their potential for application in the treatment of major functional deficits in children with DS.

Assessing cognitive improvement in people with Down syndrome: important considerations for drug-efficacy trials

Experimental research over just the past decade has raised the possibility that learning deficits connected to Down syndrome (DS) might be effectively managed by medication. In the current chapter, we touch on some of the work that paved the way for these advances and discuss the challenges associated with translating them. In particular, we highlight sources of phenotypic variability in the DS population that are likely to impact performance assessments. Throughout, suggestions are made on how to detect meaningful changes in cognitive-adaptive function in people with DS during drug treatment. The importance of within-subjects evaluation is emphasized.

Triplication of DYRK1A causes retinal structural and functional alterations in Down syndrome

Down syndrome (DS) results from the triplication of approximately 300 human chromosome 21 (Hsa21) genes and affects almost all body organs. Children with DS have defects in visual processing that may have a negative impact on their daily life and cognitive development. However, there is little known about the genes and pathogenesis underlying these defects. Here, we show morphometric in vivo data indicating that the neural retina is thicker in DS individuals than in the normal population. A similar thickening specifically affecting the inner part of the retina was also observed in a trisomic model of DS, the Ts65Dn mouse. Increased retinal size and cellularity in this model correlated with abnormal retinal function and resulted from an impaired caspase-9-mediated apoptosis during development. Moreover, we show that mice bearing only one additional copy of Dyrk1a have the same retinal phenotype as Ts65Dn mice and normalization of Dyrk1a gene copy number in Ts65Dn mice completely rescues both, morphological and functional phenotypes. Thus, triplication of Dyrk1a is necessary and sufficient to cause the retinal phenotype described in the trisomic model. Our data demonstrate for the first time the implication of DYRK1A overexpression in a developmental alteration of the central nervous system associated with DS, thereby providing insights into the aetiology of neurosensorial dysfunction in a complex disease.

Multiple-object tracking among individuals with Down syndrome and typically developing children

We investigated differences in multiple-object tracking among individuals with Down syndrome (DS) as compared to typically developing children matched on a visual–spatial mental age of approximately 5.5 years. In order to ensure that these effects did not originate in differences in encoding or reporting the positions of targets in distracters after a delay, immediate and delayed report were measured for static items. Although their immediate and delayed report for multiple static items was comparable to that of the typically developing children, the participants with DS performed as if they were only capable of tracking a single item at a time regardless of the number of targets that needed to be tracked. This finding is surprising because the operations used in multiple-object tracking are thought to be necessary for visuospatial tasks, which are an area of relative strength among persons with DS. These results call into question the idea that abilities or deficits in multiple-object tracking predict visuospatial performance, and highlight ways that atypical development can inform our understanding of typical development.

Avaliação da sensibilidade ao contraste em pacientes com migrânea

O objetivo foi medir a Função de Sensibilidade ao Contraste (FSC) de pacientes com migrânea e de voluntários saudáveis sem a patologia. Participaram dos testes 12 voluntários do sexo feminino, seis com migrânea e seis sem migrânea na faixa etária de 20 a 37 anos. As medidas de FSC foram realizadas utilizando estímulos visuais estáticos de grades senoidais angulares com frequências espaciais de 2, 3, 4, 24 e 64 ciclos/360º Foi utilizado o método psicofísico da escolha forçada entre duas alternativas temporais, condições de luminância fotópica (luminância média da tela de 41 cd/m²) e visão binocular com pupila natural. Os resultados demonstram que a percepção visual de contraste dos voluntários com migrânea foi menor nas frequências de 2, 3, 4 e 64 ciclos/360º. Esses achados preliminares sugerem alterações na FSC relacionadas a essa patologia.

Time and frequency analysis of the static balance in young adults with Down syndrome

The main objective of this study is to understand the differences in equilibrium control between normal subjects and those with Down syndrome. A total of 54 subjects participated voluntarily, divided into control group and Down syndrome group. The equilibrium of the subjects was tested under two conditions: bipedal support with eyes open and closed. The signals were analyzed in a time and frequency domain. The statistical parameters selected (i.e., RMS distance, mean velocity, mean frequency and sway area) to analyze the behavior of the center of pressures (CoP) are calculated employing the result of the combination of the time series data in both directions (i.e. resultant distance). In order to calculate the frequency bands produced by the displacements of the CoP, a Fast Fourier Transform of the data was performed. The group with Down syndrome showed poorer static equilibrium control than the control group in the time domain. In the frequency domain, we found differences between the groups in the distribution of energy in the frequency bands analyzed. In addition, we observed the existence of an interaction effect of the group and the condition tested (p<0.001). These findings show that in the absence of visual information, the control group increases the energy at low frequencies, while the group with Down syndrome decreases it. Additionally, the lower amount of energy observed in this band under the 'eyes closed' condition may serve to identify abnormalities in the functioning of the vestibular apparatus of individuals with Down syndrome and/or difficulties experienced by these individuals in extracting relevant information from this route.

Corneal power and astigmatism in Down syndrome

PURPOSE

Corneal and crystalline lens shape differ in Down syndrome (DS) compared with developmentally normal populations. This study specifically explored the association between corneal curvature and refractive error for the first time in DS.

METHODS

Participants were 29 children with 59 age-matched controls (33 males and 35 females; mean age 12.4 +/- 1.8 years) and DS (9 to 16 years; 19 males and 10 females; mean age 12.8 +/- 1.9 years). Corneal curvature was measured using a hand-held keratometer. Refractive error was assessed by distance static retinoscopy in the control group and Mohindra retinoscopy in the DS group.

RESULTS

The DS group demonstrated a high frequency and magnitude of refractive errors (mean DS + 2.52 +/- 3.00 D; mean controls -0.46 +/- 1.32 D). The majority of controls had little or no significant refractive error. DS cornea were significantly steeper (mean DS 45.62 +/- 2.13 D; mean controls 43.10 +/- 1.37 D). Neither DS nor control data demonstrate significant relations between corneal and total refractive power (M vector). Astigmatic errors in the DS group were more frequently oblique and demonstrated strong right-left specificity. The DS data did not demonstrate a significant association between corneal and total astigmatism along principal meridians (J0), however, a significant relation was found for the control data (linear regression, r = 0.51, p < 0.0001). No significant association between corneal and total oblique astigmatism (J45) was demonstrated by either DS or control data.

CONCLUSIONS

The study is the first to explicitly investigate the association between corneal power and refractive error in children with DS. The majority of the DS group have significant refractive errors including an increased prevalence of oblique astigmatism. Corneal curvature in DS is not related to spherical (M) or astigmatic (J0, J45) refractive error. Further research is required to better understand the association between the ocular structures of the DS eye and their impact on functional vision.

Ophthalmic abnormalities in children with Down syndrome

A comprehensive review of the available literature was performed to determine the common ophthalmic disorders in children aged 0 to 16 years with Down syndrome. The UK National Library for Health interface was used to search seven electronic databases, including MEDLINE and EMBASE. Terms related to Down syndrome, ophthalmology, and pediatrics were combined in the search strategy, which yielded 230 articles. Application of exclusion criteria left 23 articles to include in the review. Literature synthesis demonstrated that children with Down syndrome are at risk for several ocular disorders. Refractive error was a common finding, particularly hyperopia. Strabismus was also reported regularly, particularly esodeviation. Other frequent findings included poor visual acuity, nystagmus, and blepharitis, whereas cataract and glaucoma were less common but had potentially serious implications for future vision. Only one study compared routine pediatric examination to that of a pediatric ophthalmologist. The findings of this review confirm the need for an ophthalmic screening program for children with Down syndrome. Additional work should investigate how such a program could be best implemented and ascertain how to involve different professionals in such a service.

Strategy adoption and locomotor adjustment in obstacle clearance of newly walking toddlers with Down syndrome after different treadmill interventions

This study investigated how newly walking toddlers with Down syndrome (DS), after different treadmill interventions, adopted clearance strategies and modified anticipatory locomotor adjustment patterns to negotiate an obstacle in their travel path. Thirty infants with DS (about 10 months of age) were recruited and randomly assigned to either a lower-intensity, generalized (LG) treadmill training group, or a higher-intensity, individualized (HI) treadmill training group. Thirteen in each group completed a one-year-gait follow-up after the treadmill intervention. Initially, both groups chose to either crawl or walk over an obstacle. However, walking over the obstacle became their preferred clearance strategy over the course of the gait follow-up even though the height of the obstacle increased from visit to visit. The HI group used the strategy of walking over the obstacle at a considerably higher percentage than the LG group within 6 months after the training. When approaching the obstacle, both groups started to show consistent anticipatory locomotor adjustments about 6 months after the training. Both groups decreased velocity, cadence and step length, and increased step width at the last three pre-obstacle steps. It was concluded that the retention of the HI training effects led the HI group to predominantly walk over an obstacle earlier than the LG group within 6 months after treadmill intervention, and the two groups produced similar anticipatory locomotor adjustments in the last three steps before negotiating the obstacle.

Association between accommodative accuracy, hypermetropia, and strabismus in children with Down's syndrome

PURPOSE

A significant proportion of children with Down's syndrome have been shown to have reduced accommodation. The purpose of this study was to investigate any association between reduced accommodation and refractive error, strabismus, visual acuity, and other ocular parameters.

METHODS

Subjects were children with Down's syndrome enrolled in a longitudinal cohort to monitor visual development. Twenty-seven children with accurate accommodation were age-matched to children with reduced accommodation based on their most recent assessment for which a full, reliable data set was available. Each child was used only once for matching. Cross-sectional ocular and visual data were analyzed using chi or Fisher's exact test, or the Mann-Whitney U test for (non-normally distributed) quantitative data.

RESULTS

Children with under-accommodation were statistically more likely to have moderate/high hypermetropia (> or = +3.00 D) and to be strabismic (most with esotropia). No significant difference between the groups was found for any other ocular parameters.

CONCLUSIONS

This study demonstrates the marked association between under-accommodation, hypermetropia, and strabismus in children with Down's syndrome. No causal relation can be demonstrated with these data, but findings suggest that the link between under-accommodation and hypermetropia (and between accurate accommodation and emmetropia) is present in early infancy.

Contrast sensitivity in seasonal and nonseasonal depression

BACKGROUND

Psychophysics has been used for the early diagnosis of many diseases that affect the visual pathway including those not usually considered vision-related (e.g., Parkinson's disease). Little has been done, however, to investigate visual functioning in psychological disorders known to be effectively treated by phototherapy. We measured the static and dynamic spatial contrast detection thresholds of seasonally depressed (SAD), nonseasonally depressed (Depressed) and nondepressed (Control) individuals.

METHODS

Two psychophysical experiments which measured luminance contrast detection thresholds were conducted. Experiment 1 presented static, vertically oriented Gabors with center spatial frequencies ranging from 0.3 to 12.0 cpd (cycles per degree). Experiment 2 presented 0.5, 1.5 and 4.0 cpd Gabors whose phases were sinusoidally reversed at 2.0, 4.0, 8.0, 16.0, and 32.0 c/s (Hz).

RESULTS

SAD showed significantly greater contrast sensitivities than Controls for static spatial frequencies equal to or greater than 6.0 cpd. Depressed showed significantly greater contrast sensitivities at 6.0 cpd and 12.0 cpd. With phase modulation, the SAD group showed significantly enhanced contrast sensitivity with 4.0 cpd-2.0 Hz Gabors. All other results at lower spatial-higher temporal frequencies were not significant.

LIMITATIONS

Most of the subjects were drawn from the student population instead of the community or clinics, even though they met the criteria for clinical depression. Antidepressant use was not controlled for among the subjects.

CONCLUSIONS

These findings suggest that clinical depression can enhance contrast sensitivity when stimuli elicit strong parvocellular responses. These enhancements implicate differences in retinal functionality. Mechanisms that link neuromodulatory activity to retinal signal processing are proposed.

Accuracy of the contrast sensitivity card test for infants: retest variability and prediction of spatial resolution

PURPOSE

We assessed the retest variability of a new contrast sensitivity (CS) card procedure and its ability to predict spatial resolution.

METHODS

Twenty-four 3-month-olds were tested twice with the CS cards and once with the Teller acuity cards (TAC) within a single session.

RESULTS

Coefficient of repeatability (COR) analysis revealed that retest variability of the new cards is superior to that of an earlier prototype at low to mid spatial frequencies. Furthermore, retest variability is comparable to that of infant visual evoked potential studies and the Vistech 6500, a chart commonly used to measure CS in adults. Finally, estimates of visual acuity based on the CS cards were consistent with those provided by the TAC (although CS-based estimates were generally lower overall).

CONCLUSIONS

Given its reliability and accuracy, the new CS card procedure has good potential as a clinical tool for assessing spatial vision in infants and toddlers.

Medidas psicofísicas e eletrofisiológicas da função visual do recém nascido: uma revisão

O sistema visual apresenta muitas funções ao nascimento. O processo de amadurecimento destas funções demanda um tempo variado. Neste trabalho, inicialmente descreveremos como a psicofísica e a eletrofisiologia visual tem colaborado para a medida e o estudo do desenvolvimento de três funções visuais: acuidade visual, sensibilidade ao contraste e visão de cores. Num segundo momento, discutimos sobre como a medida e o desenvolvimento destas funções podem estar prejudicados em patologias que afetam o sistema visual, como a prematuridade e a paralisia cerebral.

Chromatic and achromatic transient VEPs in adults with Down syndrome

Oculo-visual abnormalities such as strabismus and high refractive error are common in people with Down syndrome, and account in large part for reduced visual function in this group. In the absence of such abnormalities, however, some spatial vision deficits persist, probably reflecting abnormal function of the neural visual pathway in this population. In addition, colour vision abnormalities are reportedly common in subjects with Down syndrome. We recorded transient visual evoked potentials in response to black-white and chromatic stimuli, in seven subjects with Down syndrome and 33 controls, to investigate function of the visual pathways underpinning spatial and chromatic visual function in Down syndrome. Our findings indicate, in agreement with previous studies, that retino-striate achromatic and chromatic processing in Down syndrome are abnormal. We find, however, that abnormal retino-striate processing of chromatic signals in this group may not give rise to colour vision deficits detected by the Colour Vision Test Made Easy or the City University test.

Transient pattern Visual Evoked Potentials in children with Down's syndrome

Visual acuity and contrast sensitivity are lower in children with Down's syndrome than in those developing normally. In many cases, this difference might be accounted for by the relatively high incidence of ocular abnormalities (including refractive error and strabismus) in Down's syndrome. However, abnormal spatial vision persists in children with Down's syndrome in the absence of ocular abnormality, suggesting that abnormal retino-cortical visual processing explains reduced visual function in this group. The aim of the present study was to assess retino-cortical function in children with Down's syndrome by recording transient visual evoked potentials (VEPs) in response to pattern stimuli. Responses from children with Down's syndrome were compared with those recorded from children developing normally. Response latency is similar in the two groups, but morphology differs, with the N75 component being clearly present in the normal responses, but diminished or undetectable in responses from children with Down's syndrome. Our findings may suggest a cortical abnormality specific to the source of the N75 component of pattern-reversal achromatic VEPs.

A double-masked, randomized control trial of iron supplementation in early infancy in healthy term breast-fed infants

OBJECTIVES

To test whether iron supplementation affects hematologic, biochemical, and developmental status in term breast-fed infants.

STUDY DESIGN

Term breast-fed infants (n=77) were randomly selected to receive either 7.5 mg per day of elemental iron as ferrous sulfate or placebo from 1 to 6 months of age. Investigators and families were unaware of group assignment. Complete blood count and ferritin, red cell superoxide dismutase, catalase, plasma ferric reducing antioxidant power, and zinc and copper levels were analyzed at 1, 3.5, 6, and 12 months of age. Bayley mental and psychomotor developmental indexes (MDI and PDI) and visual acuity (with the use of Teller acuity cards) were assessed from 12 to 18 months of age. Analysis performed by analysis of variance and t tests was by intention to treat.

RESULTS

Iron supplementation resulted in higher hemoglobin and mean corpuscular volume at 6 months of age and significantly higher visual acuity and PDI at 13 months of age (100+/-12 vs 93+/-9 [+/-SD]). Treatment and placebo groups did not differ in anthropometric indexes, compliance, biochemical status, or demographic characteristics.

CONCLUSIONS

Iron supplementation of breast-fed infants appears safe and might have beneficial hematologic and developmental effects for some infants.

Comparison of different therapy approaches in children with Down syndrome

BACKGROUND

Children with Down syndrome have sensory integrative dysfunction as a result of limited sensory experience from lack of normal motor control. The aim of the present study was to compare the effects of sensory integrative therapy alone, vestibular stimulation in addition to sensory integrative therapy and neurodevelopmental therapy, on children with Down syndrome.

METHODS

The present study was carried out at the Occupational Therapy Unit, School of Physical Therapy and Rehabilitation of Hacettepe University. Forty-five children who were diagnosed as having Down syndrome by the Departments of Paediatric Neurology and Medical Genetics at Hacettepe University were assessed and randomly divided into three groups. Sensory integrative therapy was given to the first group (n=15), vestibular stimulation in addition sensory integrative therapy was given to the second group (n=15) and neurodevelopmental therapy was given to the third group (n=15). All children were evaluated with Ayres Southern California Sensory Integration Test, Pivot Prone Test, Gravitational Insecurity Test and Pegboard Test. The hypotonicity of extensor muscles, joint stability, automatic movement reactions and locomotor skills were tested. Treatment programs were 1.5 h per session, 3 days per week for 3 months.

RESULTS

When these groups were compared, statistically significant differences were found in subjects' performance of balance on right foot-eyes open, pivot prone position-quality score and locomotor skills-front tests (P<0.05). There were no significant differences in the other tests (P>0.05).

CONCLUSIONS

The results of the present study showed that sensory integration, vestibular stimulation and neurodevelopmental therapy were effective in children with Down syndrome. It was concluded that when designing rehabilitation programs for children with Down syndrome, all treatment methods should be applied in combination, and should support each other according to the individual needs of the child.

Prehension in young children with Down syndrome

Prehension was examined in 3-year old children with Down syndrome (DS, n = 3) and in typically-developing children matched in chronological age (3-year olds; n = 3) or mental age and motor experience (2-year olds; n = 3). The task required reaching to grasp dowels. Video-based movement analysis yielded temporal and kinematic measures. Children with DS were hypothesized to have deficits in feedback-dependent components of prehension (anticipatory grip-closure and deceleration of reach), whereas feedforward components (reach's acceleration phase; grasp's preshaping) were assumed to be unimpaired [Latash, 1993, Control of human movement, pp. 283-292; Latash, 1994, What is clumsiness? In: Motor Control and Down Syndrome II Proceedings of the second international conference, pp. 68-71]. The findings supported these hypotheses. In comparison to control groups, children with DS had significantly: (a) less time in deceleration of reaching, (b) fewer anticipatory grip-closures, and (c) longer movement times for dowel-lift. Young children with DS appeared to use dowel-contact to decelerate the limb and initiate grip-closure. In contrast, reach-acceleration time and grasp-preshaping did not differ across groups. These findings suggest that children with DS display qualitative differences in motor capabilities rather than simply a delayed rate of typical developmental progression.

Improving the effectiveness of the infant contrast sensitivity card procedure

Based on results from an earlier prototype, custom software and printing techniques were developed to construct a new card-based test of contrast sensitivity (CS) for nonverbal subjects. Compared with the prototype, the new CS card test contains three improvements: (1) larger, more salient test gratings; (2) higher contrast warm-up cards for each spatial frequency set; and (3) smaller contrast step size between adjacent cards. The success of the new cards was evaluated by testing 3.5- and 12-month-old human infants. Results indicated that the new version of the test required little time to complete (mean, 6.5 min) and provided accurate estimates of visual acuity. Also, group contrast sensitivity functions (CSFs) showed substantial development from 3.5 to 12 months of age. Surprisingly, however, group CSFs obtained with the new cards were lower than those obtained with the prototype, a discrepancy that may be due to differences in space average luminance between the two sets of cards. In all, the new CS card procedure possesses several merits that give it potential as an option for assessing spatial vision in infants, toddlers, and subjects with multiple impairments.

Retest variability of human infant contrast sensitivity: how many tests are sufficient?

Retest variability of a new infant contrast sensitivity (CS) card procedure was assessed by binocular measurement of a group of 20 6-month-olds twice within a 1-week period. Coefficient of reliability analyses showed that within-subject variability between tests was only slightly less than variation across subjects, which suggests that results from a single test are a poor predictor of an infant's "true" visual functioning. To determine how many tests are needed to estimate when infant CS stabilizes to within an acceptable (0.15 log unit) criterion, a second experiment was conducted in which a small group of subjects was tested repeatedly over a 2-week period. The results showed that averaging performance on 2 to 3 tests was required before an accurate estimate of the subject's performance could be obtained. Our results suggest that caution should be taken in the interpretation of a single measurement of infant visual functioning.