When children have visual and/or oculomotor deficits, early diagnosis is critical for rehabilitation. The developmental eye movement (DEM) test is a visual-verbal number naming test that aims to measure oculomotor dysfunction in children by comparing scores on a horizontal and vertical subtest. However, empirical comparison of oculomotor behavior during the two subtests is missing. Here, we measured eye movements of healthy children while they performed a digital version of the DEM. In addition, we measured visual processing speed using the Speed Acuity test. We found that parameters of saccade behavior, such as the number, amplitude, and direction of saccades, correlated with performance on the horizontal, but not the vertical subtest. However, the time spent on making saccades was very short compared to the time spent on number fixations and the total time needed for either subtest. Fixation durations correlated positively with performance on both subtests and co-varied tightly with visual processing speed. Accordingly, horizontal and vertical DEM scores showed a strong positive correlation with visual processing speed. We therefore conclude that the DEM is not suitable to measure saccade behavior, but can be a useful indicator of visual-verbal naming skills, visual processing speed, and other cognitive factors of clinical relevance.

Traditional video-based eyetrackers require participants to perform an individual calibration procedure, which involves the fixation of multiple points on a screen. However, certain participants (e.g., people with oculomotor and/or visual problems or infants) are unable to perform this task reliably. Previous work has shown that with two cameras one can estimate the orientation of the eyes’ optical axis directly. Consequently, only one calibration point is needed to determine the deviation between an eye’s optical and visual axes. We developed a stereo eyetracker with two USB 3.0 cameras and two infrared light sources that can track both eyes at ~ 350 Hz for eccentricities of up to 20°. A user interface allows for online monitoring and threshold adjustments of the pupil and corneal reflections. We validated this tracker by collecting eye movement data from nine healthy participants and compared these data to eye movement records obtained simultaneously with an established eyetracking system (EyeLink 1000 Plus). The results demonstrated that the two-dimensional accuracy of our portable system is better than 1°, allowing for at least ± 5-cm head motion. Its resolution is better than 0.2° (SD), and its sample-to-sample noise is less than 0.05° (RMS). We concluded that our stereo eyetracker is a valid instrument, especially in settings in which individual calibration is challenging.Electronic supplementary materialThe online version of this article (10.3758/s13428-018-1026-7) contains supplementary material, which is available to authorized users.

Our data revealed substantial developmental improvements in visual discrimination speed, which suggests that an important optimization takes place in the developing visual system of 5- to 12-year-old children. Since the speed-acuity test allows for quick and reliable assessment of visual recognition acuity and speed, it may be useful in clinical testing too.

Citation: Barsingerhorn AD, Boonstra FN, Goossens J. Symbol discrimination speed in children with visual impairments. Invest Ophthalmol Vis Sci. 2018;59:3963-3972. https://doi.org/ 10.1167/iovs.17-23167 PURPOSE. We measured visual acuity and visual discrimination speed simultaneously in children with visual impairments to determine whether they are slower than children with normal vision.METHODS. Five-to twelve-year-old children with visual impairments due to ocular dysfunction (VI o ; n ¼ 30) or cerebral visual impairment (CVI; n ¼ 17) performed a speed-acuity test in which they indicated the orientation of Landolt-C symbols as quickly and accurately as possible. The reaction times for symbols ranging between À0.3 and 1.2 logMAR relative to acuity threshold were compared with normative data. To test whether children were already slow in merely detecting symbols, we also compared their reaction times on a simple visual detection task (VDT) to normative data. An auditory detection task (ADT) was used to probe for other, more general deficits. RESULTS.Of the children with visual impairments, 88% had abnormally long reaction times in the speed-acuity test. This deficit was partly explained by their reduced acuity, but 40% still needed more time to discriminate acuity-matched optotypes. Children responded late in the VDT too, especially those with CVI, but this impairment could not fully account for their slow symbol discrimination. In children with CVI, reaction times in the ADT were affected as much as those in the VDT, suggesting more general sensorimotor problems in CVI.CONCLUSIONS. The speed-acuity test offers additional insight in visual impairment. Children with VI o and CVI are abnormally slow in discerning foveal details. Magnification of materials is often insufficient to compensate for this deficit, partly because stimulus detection is already hampered.