Beyond visual acuity: Development of visual processing speed and quantitative assessment of visual impairment in children

Contains fulltext : 195501.pdf (publisher's version ) (Open Access)Radboud University, 31 oktober 2018Promotor : Opstal, A.J. van Co-promotores : Goossens, H.H.L.M., Boonstra, F.N.224 p

Saccade latencies during a preferential looking task and objective scoring of grating acuity in children with and without visual impairments

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Development and validation of a high-speed stereoscopic eyetracker

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Symbol Discrimination Speed in Children With Visual Impairments

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Optics of the human cornea influence the accuracy of stereo eye-tracking methods: a simulation study

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

The Developmental Eye Movement test does not detect oculomotor problems: Evidence from children with nystagmus

SIGNIFICANCE: The Developmental Eye Movement (DEM) test, a test purported to assess oculomotor skills, does not detect eye movement disorder in nystagmus syndromes. The test should not be used for the clinical evaluation of oculomotor disorders. PURPOSE: The DEM test ratio compares a horizontal number naming subtest with a vertical one to identify oculomotor problems independent of a child's visual-verbal naming skills. Here, we tested the construct validity of this method by comparing scores of children with and without pathologic nystagmus. Such a nystagmus disturbs normal fixation and saccadic behavior because of the presence of involuntary rhythmic oscillations of the eyes. Therefore, if the ratio is indeed a comprehensive measure of oculomotor problems, children with nystagmus should show an increased ratio score. METHODS: The DEM test performances of normally sighted children (n = 94), children with ocular visual impairments (VIo; n = 33), and children with cerebral visual impairment (n = 30) were analyzed using linear regression. Part of the children with VIo and cerebral visual impairment had either fusion maldevelopment nystagmus syndrome (n = 8) or infantile nystagmus syndrome (n = 20), whereas the others showed no pathologic nystagmus. RESULTS: The times needed for the horizontal and vertical subtests were significantly different between children with normal vision, VIo, and cerebral visual impairment (P .20), nor did it have an effect on the ratio (P > .10). CONCLUSIONS: The DEM test ratio is not sensitive to fixation and saccade abnormalities associated with nystagmus, indicating that it does not have general construct validity to detect true eye movement disorders. Although not suitable for the evaluation of oculomotor disorders, the subtests do have clinical relevance in the diagnosis of cerebral visual impairment

The Developmental Eye Movement Test as a Diagnostic Aid in Cerebral Visual Impairment

The symptoms that characterize children with cerebral visual impairments (CVI) are diverse, ranging from extensive behavioral or physical disabilities to subtle changes that can easily be missed. A correct diagnosis of CVI is therefore difficult to make, but having a wide variety of tests available can be helpful. This study aims to determine if the developmental eye movement test (DEM) can be one of those tests. In this test, a fixed set of numbers has to be read aloud, first in vertical columns and then in horizontal lines. In order to measure differences between children with CVI compared to normally sighted age-matched controls and children with a visual impairment (VI), we determined DEM times, crowding intensities and the reaction time to a large visual stimulus for all three groups. We found that children with CVI or VI need significantly more time to read the DEM numbers than age-matched controls. Additionally, children with CVI need more time than children with VI to read the horizontal DEM, but not the vertical DEM. We also found a significant difference between the children with CVI and the other two groups in the relationship between horizontal DEM performance and crowding intensity. However, for the relationship between DEM performance and visual detection time, no group-differences were found. We conclude that the DEM can be a useful addition in the diagnosis of CVI, especially in combination with information about crowding

The speed acuity test as a diagnostic aid in cerebral visual impairment

One of the characteristics of children with cerebral visual impairments (CVI) is that they need more time to process visual information. However, currently, few tests are available that can reliably measure visual processing speed. The speed acuity test, a discrimination reaction-time test in which participants indicate the orientation of Landolt-C symbols as quickly and accurately as possible, was specifically developed to determine the time a child needs to discern visual details. The test measures both the accuracy and the latency of the responses for nine different optotype sizes in order to control for decreased visual acuity. The results show that children with CVI need significantly more time to respond to the largest optotype sizes than age-matched normally sighted children and children with visual impairments due to an ocular disorder (VIo). This effect is independent of the time it takes to make a motor response. However, the reaction-time difference between the children with CVI and VIo is not seen for optotype sizes at the acuity threshold. Together with reaction times on visual and auditory detection tasks as controls, reaction times measured in the speed-acuity test allow for acceptable discrimination (AUC in ROC analysis: 0.81) between CVI and VIo

Visual fixations rather than saccades dominate the developmental eye movement test

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