Bianca Huurneman

Crowding in Central Vision in Normally Sighted and Visually Impared Children Aged 4 to 8 Years: The Influence of Age and Test Design

Background/aims: To investigate crowding ratios in children with a visual impairment due to ocular disease (n = 58) and normally sighted children (n = 75) aged 4 to 8 years using several variants of two clinically available tests with different optotype spacing (fixed or proportional to the optotype size). Methods: Crowding ratios, calculated by dividing the single acuity by the linear acuity, were measured binocularly with the C-test and the LH line chart. Ratios >1.00 indicate crowding. Results: The charts with fixed spacing revealed significantly higher crowding ratios for visually impaired children than normally sighted children (both for measurements at 40 cm and 5 m). The age-related reduction of the crowding ratios seen in normally sighted children when tested with near-vision charts with fixed spacing was not present in the visually impaired group. Visually impaired children with nystagmus showed higher crowding ratios than visually impaired children without nystagmus. The chart with proportional intersymbol spacing (ISS) did not reveal differences between the normally sighted and visually impaired children; nor did it show group, age, or nystagmus effects. Conclusion: Visually impaired children showed higher crowding ratios than normally sighted children when measured with charts with fixed ISS. This study illustrates that test design and target/flanker interference as a manifestation of crowding are critical issues to bear in mind when assessing crowding ratios in children.

A systematic review on ‘Foveal Crowding’ in visually impaired children and perceptual learning as a method to reduce Crowding

BackgroundThis systematic review gives an overview of foveal crowding (the inability to recognize objects due to surrounding nearby contours in foveal vision) and possible interventions. Foveal crowding can have a major effect on reading rate and deciphering small pieces of information from busy visual scenes. Three specific groups experience more foveal crowding than adults with normal vision (NV): 1) children with NV, 2) visually impaired (VI) children and adults and 3) children with cerebral visual impairment (CVI). The extent and magnitude of foveal crowding as well as interventions aimed at reducing crowding were investigated in this review. The twofold goal of this review is : [A] to compare foveal crowding in children with NV, VI children and adults and CVI children and [B] to compare interventions to reduce crowding.MethodsThree electronic databases were used to conduct the literature search: PubMed, PsycINFO (Ovid), and Cochrane. Additional studies were identified by contacting experts. Search terms included visual perception, contour interaction, crowding, crowded, and contour interactions.ResultsChildren with normal vision show an extent of contour interaction over an area 1.5–3× as large as that seen in adults NV. The magnitude of contour interaction normally ranges between 1–2 lines on an acuity chart and this magnitude is even larger when stimuli are arranged in a circular configuration. Adults with congenital nystagmus (CN) show interaction areas that are 2× larger than those seen adults with NV. The magnitude of the crowding effect is also 2× as large in individuals with CN as in individuals with NV. Finally, children with CVI experience a magnitude of the crowding effect that is 3× the size of that experienced by adults with NV.ConclusionsThe methodological heterogeneity, the diversity in paradigms used to measure crowding, made it impossible to conduct a meta-analysis. This is the first systematic review to compare crowding ratios and it shows that charts with 50% interoptotype spacing were most sensitive to capture crowding effects. The groups that showed the largest crowding effects were individuals with CN, VI adults with central scotomas and children with CVI. Perceptual Learning seems to be a promising technique to reduce excessive foveal crowding effects.

Perceptual Learning in Children With Visual Impairment Improves Near Visual Acuity

PURPOSE This study investigated whether visual perceptual learning can improve near visual acuity and reduce foveal crowding effects in four- to nine-year-old children with visual impairment. METHODS Participants were 45 children with visual impairment and 29 children with normal vision. Children with visual impairment were divided into three groups: a magnifier group (n = 12), a crowded perceptual learning group (n = 18), and an uncrowded perceptual learning group (n = 15). Children with normal vision also were divided in three groups, but were measured only at baseline. Dependent variables were single near visual acuity (NVA), crowded NVA, LH line 50% crowding NVA, number of trials, accuracy, performance time, amount of small errors, and amount of large errors. Children with visual impairment trained during six weeks, two times per week, for 30 minutes (12 training sessions). RESULTS After training, children showed significant improvement of NVA in addition to specific improvements on the training task. The crowded perceptual learning group showed the largest acuity improvements (1.7 logMAR lines on the crowded chart, P < 0.001). Only the children in the crowded perceptual learning group showed improvements on all NVA charts. CONCLUSIONS Children with visual impairment benefit from perceptual training. While task-specific improvements were observed in all training groups, transfer to crowded NVA was largest in the crowded perceptual learning group. To our knowledge, this is the first study to provide evidence for the improvement of NVA by perceptual learning in children with visual impairment. (http://www.trialregister.nl number, NTR2537.).

Crowded visual search in children with normal vision and children with visual impairment

This study investigates the influence of oculomotor control, crowding, and attentional factors on visual search in children with normal vision ([NV], n=11), children with visual impairment without nystagmus ([VI-nys], n=11), and children with VI with accompanying nystagmus ([VI+nys], n=26). Exclusion criteria for children with VI were: multiple impairments and visual acuity poorer than 20/400 or better than 20/50. Three search conditions were presented: a row with homogeneous distractors, a matrix with homogeneous distractors, and a matrix with heterogeneous distractors. Element spacing was manipulated in 5 steps from 2 to 32 minutes of arc. Symbols were sized 2 times the threshold acuity to guarantee visibility for the VI groups. During simple row and matrix search with homogeneous distractors children in the VI+nys group were less accurate than children with NV at smaller spacings. Group differences were even more pronounced during matrix search with heterogeneous distractors. Search times were longer in children with VI compared to children with NV. The more extended impairments during serial search reveal greater dependence on oculomotor control during serial compared to parallel search.

Effects of magnifier training: Evidence from a camera built in the magnifier

Purpose: This study evaluated the effect of an evidence-based magnifier training on viewing behavior in visually impaired children aged 3 to 6½ years. Methods: Effects of a training with a stand magnifier were evaluated by analyzing recordings of 21 visually impaired children, obtained from a miniature camera mounted in the magnifier. In a pre-test, post-test design, 11 of the children trained without magnifier and 10 children trained with magnifier. Three measures were compared from pre- to post-test assessment: 1) observation time in seconds through the magnifier during task performance; 2) the eye that was used during task performance with the magnifier (right eye/left eye as recorded by the camera); and 3) the self-chosen eye-to-chart distance (in cm) in near visual acuity measurement. Results: Three important changes were found by analyzing the eye-camera recordings: (1) There was a significant shift in average observation time (i.e., the duration of looking through the magnifier in a single glance), before and after training. In the pre-test children used less than 10 s for a glance through the magnifier, whereas in the post-test this was 10–30 s.(2) In 5 children there was no preference with respect to the number of glances through the magnifier with right or left eye during pre-test measurement. However, such a task-specific dominance was clearly observed in this subgroup after training (post-test measurement).(3) The eye-to-chart distance, as measured during near-vision testing with LH-single and LH-line test, decreased significantly over the training period (from 9.5 cm to 7.9 cm, pre- to post-test). There were no differences in the outcome measures between the with-magnifier and without-magnifier training groups. We can conclude that (1) the magnifier training had a positive effect on viewing behavior and the development of dominance, and (2) camera observations provide valuable data on children’s viewing behavior.

Perceptual Learning in Children With Infantile Nystagmus: Effects on Reading Performance

PURPOSE To evaluate whether computerized training with a crowded or uncrowded letter-discrimination task reduces visual impairment (VI) in 6- to 11-year-old children with infantile nystagmus (IN) who suffer from increased foveal crowding, reduced visual acuity, and reduced stereopsis. METHODS Thirty-six children with IN were included. Eighteen had idiopathic IN and 18 had oculocutaneous albinism. These children were divided in two training groups matched on age and diagnosis: a crowded training group (n = 18) and an uncrowded training group (n = 18). Training occurred two times per week during 5 weeks (3500 trials per training). Eleven age-matched children with normal vision were included to assess baseline differences in task performance and test-retest learning. Main outcome measures were task-specific performance, distance and near visual acuity (DVA and NVA), intensity and extent of (foveal) crowding at 5 m and 40 cm, and stereopsis. RESULTS Training resulted in task-specific improvements. Both training groups also showed uncrowded and crowded DVA improvements (0.10 ± 0.02 and 0.11 ± 0.02 logMAR) and improved stereopsis (670 ± 249″). Crowded NVA improved only in the crowded training group (0.15 ± 0.02 logMAR), which was also the only group showing a reduction in near crowding intensity (0.08 ± 0.03 logMAR). Effects were not due to test-retest learning. CONCLUSIONS Perceptual learning with or without distractors reduces the extent of crowding and improves visual acuity in children with IN. Training with distractors improves near vision more than training with single optotypes. Perceptual learning also transfers to DVA and NVA under uncrowded and crowded conditions and even stereopsis. Learning curves indicated that improvements may be larger after longer training.

Perceptual Learning in Children With Infantile Nystagmus: Effects on 2D Oculomotor Behavior.

PURPOSE To determine changes in oculomotor behavior after 10 sessions of perceptual learning on a letter discrimination task in children with infantile nystagmus (IN). METHODS Children with IN (18 children with idiopathic IN and 18 with oculocutaneous albinism accompanied by IN) aged 6 to 11 years were divided into two training groups matched on diagnosis: an uncrowded training group (n = 18) and a crowded training group (n = 18). Target letters always appeared briefly (500 ms) at an eccentric location, forcing subjects to quickly redirect their gaze. Training occurred twice per week for 5 consecutive weeks (3500 trials total). Norm data and test-retest values were collected from children with normal vision (n = 11). Outcome measures were: nystagmus characteristics (amplitude, frequency, intensity, and the expanded nystagmus acuity function); fixation stability (the bivariate contour ellipse area and foveation time); and saccadic eye movements (latencies and accuracy) made during a simple saccade task and a crowded letter-identification task. RESULTS After training, saccadic responses of children with IN improved on the saccade task (latencies decreased by 14 ± 4 ms and gains increased by 0.03 ± 0.01), but not on the crowded letter task. There were also no training-induced changes in nystagmus characteristics and fixation stability. Although children with normal vision had shorter latencies in the saccade task (47 ± 14 ms at baseline), test-retest changes in their saccade gains and latencies were almost equal to the training effects observed in children with IN. CONCLUSIONS Our results suggest that the improvement in visual performance after perceptual learning in children with IN is primarily due to improved sensory processing rather than improved two-dimensional oculomotor behavior.

Assessment of near visual acuity in 0–13 year olds with normal and low vision: a systematic review

BackgroundThe inclusion for rehabilitation of visually impaired children is partly based on the measurement of near vision, but guidelines for near visual acuity assessment are currently lacking. The twofold purpose of this systematic review was to: (i) provide an overview of the impact of the chart design on near visual acuity measured, and (ii) determine the method of choice for near vision assessments in children of different developmental ages.MethodsA literature search was conducted by using the following electronic databases: PubMed, Cochrane Library, and EMBASE. The last search was run on March 26th 2016. Additional studies were identified by contacting experts and searching for relevant articles in reference lists of included studies. Search terms were: vision test(s), vision assessment(s), visual acuity, chart(s) and near.ResultsFor children aged 0–3 years the golden standard is still the preferential looking procedure. Norms are available for this procedure for 6–36 month old children. For 4–7 year olds, we recommend using the LEA symbols, because these symbols have been properly validated and can be used in preliterate children. Responses can be verbal or by matching the target symbol. In children aged 8–13 years, the recommended method is the ETDRS letter chart, because letter acuity is more predictive for functional vision and reading than symbol acuity. In 8–13 year olds, letter acuity is 0.1–0.2 logMAR poorer than symbol acuity.ConclusionsChart design, viewing distance, and threshold choice have a serious impact on near visual acuity measurements. Near visual acuity measured with symbols is lower than near visual acuity measured with gratings, and near visual acuity measured with letters is lower than near visual acuity measured with symbols. Viewing distance, chart used, and letter spacing should be adapted to the child’s development and reported in order to allow comparisons between measurements.

Predictors of Sensitivity to Perceptual Learning in Children With Infantile Nystagmus

Purpose To identify predictors of sensitivity to perceptual learning on a computerized, near-threshold letter discrimination task in children with infantile nystagmus (idiopathic IN: n = 18; oculocutaneous albinism accompanied by IN: n = 18). Methods Children were divided into two age-, acuity-, and diagnosis-matched training groups: a crowded (n = 18) and an uncrowded training group (n = 18). Training consisted of 10 sessions spread out over 5 weeks (grand total of 3500 trials). Baseline performance, age, diagnosis, training condition, and perceived pleasantness of training (training joy) were entered as linear regression predictors of training-induced changes on a single- and a crowded-letter task. Results An impressive 57% of the variability in improvements of single-letter visual acuity was explained by age, training condition, and training joy. Being older and training with uncrowded letters were associated with larger single-letter visual acuity improvements. More training joy was associated with a larger gain from the uncrowded training and a smaller gain from the crowded training. Fifty-six percent of the variability in crowded-letter task improvements was explained by baseline performance, age, diagnosis, and training condition. After regressing out the variability induced by training condition, baseline performance, and age, perceptual learning proved more effective for children with idiopathic IN than for children with albinism accompanied by IN. Training gains increased with poorer baseline performance in idiopaths, but not in children with albinism accompanied by IN. Conclusions Age and baseline performance, but not training joy, are important prognostic factors for the effect of perceptual learning in children with IN. However, their predictive value for achieving improvements in single-letter acuity and crowded letter acuity, respectively, differs between diagnostic subgroups and training condition. These findings may help with personalized treatment of individuals likely to benefit from perceptual learning.

Heightened parental stress in mothers of children with visual impairment

Increased survival rates of children born preterm have led to a rise of children born with disabilities, for example retinopathy of prematurity which can cause childhood blindness. While the increased survival rate is a victory of modern-day medicine, its counterpart can be heightened parental stress for the parents of these children. Parents may be confronted when their child does not live up to their own and society’s expectations, while simultaneously these expectations may alter child behaviour and development as well. Sakkalou et al. evaluated factors affecting parental stress in mothers of children with profound and severe visual impairment at 1 and 2 years of age (T1: n=79; T2: n=73). The authors report higher parental stress levels in mothers of 1-year-old children with visual impairment (T1) than levels found in the general population. In the second year of life (T2), only mothers of children with profound visual impairment still demonstrated enhanced stress levels as indicated by clinically elevated scores (>85th percentile) on the Parenting Stress Index-Short Form. One of the strengths of the study by Sakkalou et al. is that their sample is relatively large and representative of the population of mothers of children with a congenital visual impairment. Furthermore, the study is the first to provide evidence for a relation between the severity of a child’s visual impairment and parental stress. At the same time, the authors found almost no differences between outcome measures in mothers of children with or without central nervous system disorder. The only scale for which Sakkalou et al. did find a difference was the parent-child dysfunction subscale at T1 with a higher score in the complex subgroup. Both mothers of children with severe and profound visual impairment showed enhanced scores on the parent-child dysfunction subscale at T1, which measures the parent’s perception of the parent-child relation and the child not meeting parental expectations. Another merit of the study is that it concerns longitudinal research, thus allowing for the evaluation of the hypothesis that parental stress may decrease during time as mothers become adapted to their role as a parent and have a better understanding of their child’s needs. Mothers of children with severe visual impairment did not show enhanced stress levels at T2 compared to the normative data set, supporting the hypothesis that these mothers successfully adapted to their role as parent. It would be interesting to learn more about the mechanism behind this behavioural adaptation. Although this work provides new insights into factors associated with parental stress, it also raises several questions. For example, which coping strategies do mothers of children with visual impairment use to improve interaction with their child (which may be affected by the partial or complete lack of the ability for parent and child to make eye contact)? One strategy previously described by the authors could be that mothers of children with visual impairment use more mentalizing language to stimulate social communicative skills and perspective taking. Another question concerns the impact of intervention strategies to support parents in the process of learning to meet their child’s needs (such as video-feedback interventions to promote positive parenting and information supplied by health professionals). Finally, one wonders whether the results of the study are generalizable to fathers, who play an important role in the family system. All in all, the authors have undertaken an interesting study. What the field would benefit from now is a conceptual framework in which protective factors (e.g. successful coping and adaptation strategies) and risk factors for parental stress are further specified. Identification of these factors as underlying parental stress may pave the way towards the development of successful intervention strategies to reduce stress in parents of children with a visual disability.