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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.,Radboud University Nijmegen | Huurneman B.,Institute for the Visually Impaired | Boonstra F.N.,Institute for the Visually Impaired | Cillessen A.H.N.,Radboud University Nijmegen | And 3 more authors.
Strabismus | Year: 2012

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. © 2012 Informa Healthcare USA, Inc.


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.


PubMed | Medical Center Amsterdam, Institute for the Visually Impaired, Radboud University Nijmegen and University of Groningen
Type: Journal Article | Journal: Acta ophthalmologica | Year: 2016

This study aimed to examine the controllability of cylinder-shaped and dome-shaped magnifiers in young children with visual impairment.This study investigates goal-directed arm movements in low-vision aid use (stand and dome magnifier-like object) in a group of young children with visual impairment (n=56) compared to a group of children with normal sight (n=66). Children with visual impairment and children with normal sight aged 4-8years executed two types of movements (cyclic and discrete) in two orientations (vertical or horizontal) over two distances (10cm and 20cm) with two objects resembling the size and shape of regularly prescribed stand and dome magnifiers.The visually impaired children performed slower movements than the normally sighted children. In both groups, the accuracy and speed of the reciprocal aiming movements improved significantly with age. Surprisingly, in both groups, the performance with the dome-shaped object was significantly faster (in the 10cm condition and 20cm condition with discrete movements) and more accurate (in the 20cm condition) than with the stand-shaped object.From a controllability perspective, this study suggests that it is better to prescribe dome-shaped than cylinder-shaped magnifiers to young children with visual impairment.


Bijveld M.M.C.,Institute for the Visually Impaired | Riemslag F.C.C.,Institute for the Visually Impaired | Kappers A.M.L.,University Utrecht | Hoeben F.P.,Institute for the Visually Impaired | Van Genderen M.M.,Institute for the Visually Impaired
Documenta Ophthalmologica | Year: 2011

The amplitude versus flash strength curve of 15 Hz electroretinograms (ERGs) shows two minima. The minima are caused by interactions between the primary and the secondary rod pathways (first minimum), and the secondary rod pathway and the cone-driven pathway (second minimum). Furthermore, cone pathway contributions cause higher-order harmonics to occur in the responses. We measured 15 Hz ERGs in 20 healthy subjects to determine normal ranges and in patients to verify our hypotheses on the contributions of the different pathways and to investigate the clinical application. We analyzed the amplitudes and phases of the 15, 30, and 45 Hz components in the ERGs. The overall shape of the 15 Hz amplitude curves was similar in all normal subjects and showed two minima. The 30 and 45 Hz amplitude curves increased for stimuli of high flash strengths indicating cone pathway contributions. The 15 Hz amplitude curve of the responses of an achromat was similar to that of the normal subjects for low flash strengths and showed a minimum, indicating normal primary and secondary rod pathway function. There was no second minimum, and there were no higher-order harmonics, consistent with absent cone pathway function. The 15 Hz ERGs in CSNB1 and CSNB2 patients were similar and of low amplitude for flash strengths just above where the first minimum normally occurs. We could determine that in the CSNB1 patients, the responses originate from the cone pathway, while in the CSNB2 patients, the responses originate from the secondary rod pathway. © Springer-Verlag 2011.


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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