Institute for the Visually Impaired

Zeist, Netherlands

Institute for the Visually Impaired

Zeist, Netherlands
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Barsingerhorn A.D.,Donders Institute for Brain | Boonstra F.N.,Donders Institute for Brain | Boonstra F.N.,Institute for the Visually Impaired | Goossens H.H.L.M.,Donders Institute for Brain
Biomedical Optics Express | Year: 2017

Current stereo eye-tracking methods model the cornea as a sphere with one refractive surface. However, the human cornea is slightly aspheric and has two refractive surfaces. Here we used ray-tracing and the Navarro eye-model to study how these optical properties affect the accuracy of different stereo eye-tracking methods. We found that pupil size, gaze direction and head position all influence the reconstruction of gaze. Resulting errors range between ± 1.0 degrees at best. This shows that stereo eye-tracking may be an option if reliable calibration is not possible, but the applied eye-model should account for the actual optics of the cornea. © 2017 Optical Society of America.


Huurneman B.,Donders Institute for Brain | Huurneman B.,Institute for the Visually Impaired | Boonstra F.N.,Donders Institute for Brain | Boonstra F.N.,Institute for the Visually Impaired | Goossens J.,Donders Institute for Brain
Investigative Ophthalmology and Visual Science | Year: 2017

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. © 2017 The Authors.


van de Lagemaat L.N.,University of Edinburgh | Nijhof B.,Radboud University Nijmegen | Bosch D.G.M.,Radboud University Nijmegen | Bosch D.G.M.,Institute for the Visually Impaired | And 4 more authors.
Frontiers in Neuroscience | Year: 2014

Autism spectrum disorders (ASDs) are neurodevelopmental disorders characterized by impaired social interaction and communication, and restricted behavior and interests. A disruption in the balance of excitatory and inhibitory neurotransmission has been hypothesized to underlie these disorders. Here we demonstrate that genes of both pathways are affected by ASD, and that gene expression of inhibitory and excitatory genes is altered in the cerebral cortex of adult but not younger autistic individuals. We have developed a measure for the difference in the level of excitation and inhibition based on gene expression and observe that in this measure inhibition is decreased relative to excitation in adult ASD compared to control. This difference was undetectable in young autistic brains. Given that many psychiatric features of autism are already present at an early age, this suggests that the observed imbalance in gene expression is an aging phenomenon in ASD rather than its underlying cause. © 2014 van de Lagemaat, Nijhof, Bosch, Kohansal-Nodehi, Keerthikumar and Heimel.


Huurneman B.,Institute for the Visually Impaired | Huurneman B.,Radboud University Nijmegen | Boonstra F.N.,Institute for the Visually Impaired | Cox R.F.,Institute for the Visually Impaired | And 3 more authors.
BMC Ophthalmology | Year: 2012

Background: This 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. Methods. Three 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. Results: Children 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. Conclusions: The 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. © 2012 Huurneman et al.; licensee BioMed Central Ltd.


Huurneman B.,Institute for the Visually Impaired | Huurneman B.,Radboud University Nijmegen | Cox R.F.A.,Institute for the Visually Impaired | Cox R.F.A.,University of Groningen | And 3 more authors.
Vision Research | Year: 2014

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. © 2014 Elsevier B.V.


Huurneman B.,Institute for the Visually Impaired | Huurneman B.,Radboud University Nijmegen | Boonstra F.N.,Institute for the Visually Impaired | Boonstra F.N.,Radboud University Nijmegen | And 4 more authors.
Investigative Ophthalmology and Visual Science | Year: 2013

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. © 2013 The Association for Research in Vision and Ophthalmology, Inc.


Huurneman B.,Radboud University Nijmegen | Huurneman B.,Institute for the Visually Impaired | Boonstra F.N.,Radboud University Nijmegen | Boonstra F.N.,Institute for the Visually Impaired
Strabismus | Year: 2013

Background/aims: To compare interocular acuity differences, crowding ratios, and binocular summation ratios in 4- to 8-year-old children with albinism (n = 16), children with infantile nystagmus syndrome (n = 10), and children with normal vision (n = 72). Methods: Interocular acuity differences and binocular summation ratios were compared between groups. Crowding ratios were calculated by dividing the single Landolt C decimal acuity with the crowded Landolt C decimal acuity mono- and binocularly. A linear regression analysis was conducted to investigate the contribution of 5 predictors to the monocular and binocular crowding ratio: nystagmus amplitude, nystagmus frequency, strabismus, astigmatism, and anisometropia. Results: Crowding ratios were higher under mono- and binocular viewing conditions for children with infantile nystagmus syndrome than for children with normal vision. Children with albinism showed higher crowding ratios in their poorer eye and under binocular viewing conditions than children with normal vision. Children with albinism and children with infantile nystagmus syndrome showed larger interocular acuity differences than children with normal vision (0.1 logMAR in our clinical groups and 0.0 logMAR in children with normal vision). Binocular summation ratios did not differ between groups. Strabismus and nystagmus amplitude predicted the crowding ratio in the poorer eye (p = 0.015 and p = 0.005, respectively). The crowding ratio in the better eye showed a marginally significant relation with nystagmus frequency and depth of anisometropia (p = 0.082 and p = 0.070, respectively). The binocular crowding ratio was not predicted by any of the variables. Conclusions: Children with albinism and children with infantile nystagmus syndrome show larger interocular acuity differences than children with normal vision. Strabismus and nystagmus amplitude are significant predictors of the crowding ratio in the poorer eye. © 2013 Informa Healthcare USA, Inc. All rights reserved: reproduction in whole or part not permitted.


Huurneman B.,Donders Institute for Brain | Boonstra F.N.,Donders Institute for Brain | Boonstra F.N.,Institute for the Visually Impaired | Goossens J.,Donders Institute for Brain
Investigative Ophthalmology and Visual Science | Year: 2016

PURPOSE. Perceptual learning improves visual acuity and reduces crowding in children with infantile nystagmus (IN). Here, we compare reading performance of 6- to 11-year-old children with IN with normal controls, and evaluate whether perceptual learning improves their reading. METHODS. Children with IN were divided in two training groups: a crowded training group (n = 18; albinism: n = 8; idiopathic IN: n = 10) and an uncrowded training group (n = 17; albinism: n = 9; idiopathic IN: n = 8). Also 11 children with normal vision participated. Outcome measures were: reading acuity (the smallest readable font size), maximum reading speed, critical print size (font size below which reading is suboptimal), and acuity reserve (difference between reading acuity and critical print size). We used multiple regression analyses to test if these reading parameters were related to the children’s uncrowded distance acuity and/or crowding scores. RESULTS. Reading acuity and critical print size were 0.65 6 0.04 and 0.69 6 0.08 log units larger for children with IN than for children with normal vision. Maximum reading speed and acuity reserve did not differ between these groups. After training, reading acuity improved by 0.12 6 0.02 logMAR and critical print size improved by 0.11 6 0.04 logMAR in both IN training groups. The changes in reading acuity, critical print size, and acuity reserve of children with IN were tightly related to changes in their uncrowded distance acuity and the changes in magnitude and extent of crowding. CONCLUSIONS. Our findings are the first to show that visual acuity is not the only factor that restricts reading in children with IN, but that crowding also limits their reading performance. By targeting both of these spatial bottlenecks in children with IN, our perceptual learning paradigms significantly improved their reading acuity and critical print size. This shows that perceptual learning can effectively transfer to reading. © 2016, Association for Research in Vision and Ophthalmology Inc. All rights reserved.


Huurneman B.,Donders Institute for Brain | Boonstra F.N.,Donders Institute for Brain | Boonstra F.N.,Institute for the Visually Impaired | Goossens J.,Donders Institute for Brain
Investigative Ophthalmology and Visual Science | Year: 2016

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 ¼ 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 6 4 ms and gains increased by 0.03 6 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 6 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. © 2016, Association for Research in Vision and Ophthalmology Inc. All rights reserved.


Huurneman B.,Donders Institute for Brain | Boonstra F.N.,Donders Institute for Brain | Boonstra F.N.,Institute for the Visually Impaired | Goossens J.,Donders Institute for Brain
Investigative Ophthalmology and Visual Science | Year: 2016

PURPOSE. To evaluate whether computerized training with a crowded or uncrowded letterdiscrimination 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 agematched 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 6 0.02 and 0.11 6 0.02 logMAR) and improved stereopsis (670 6 24900). Crowded NVA improved only in the crowded training group (0.15 6 0.02 logMAR), which was also the only group showing a reduction in near crowding intensity (0.08 6 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. © 2016, Association for Research in Vision and Ophthalmology Inc. All rights reserved.

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