Defective chromatic and achromatic visual pathways in developmental dyslexia: Cues for an integrated intervention programme

Chromatic visual evoked potentials: A review of physiology, methods and clinical applications

Objective assessment of the visual system can be performed electrophysiologically using the visual evoked potential (VEP). In many clinical circumstances, this is performed using high contrast achromatic patterns or diffuse flash stimuli. These methods are clinically valuable but they may only assess a subset of possible physiological circuitries within the visual system, particularly those involved in achromatic (luminance) processing. The use of chromatic VEPs (cVEPs) in addition to standard VEPs can inform us of the function or dysfunction of chromatic pathways. The chromatic VEP has been well studied in human health and disease. Yet, to date our knowledge of their underlying mechanisms and applications remains limited. This likely reflects a heterogeneity in the methodology, analysis and conclusions of different works, which leads to ambiguity in their clinical use. This review sought to identify the primary methodologies employed for recording cVEPs. Furthermore cVEP maturation and application in understanding the function of the chromatic system under healthy and diseased conditions are reviewed. We first briefly describe the physiology of normal colour vision, before describing the methodologies and historical developments which have led to our understanding of cVEPs. We thereafter describe the expected maturation of the cVEP, followed by reviewing their application in several disorders: congenital colour vision deficiencies, retinal disease, glaucoma, optic nerve and neurological disorders, diabetes, amblyopia and dyslexia. We finalise the review with recommendations for testing and future directions.

Subjective and objective evaluation of visual functions in dyslexic children with visual perceptual deficiency-Before and after ten-weeks of perceptual training

AIMS

This pilot study investigated perceptual and electrophysiological characteristics of dyslexic children, and evaluated the immediate and prolonged effect of visual perceptual training on these characteristics in these children.

METHODS AND PROCEDURES

Seven dyslexic children and seven controls aged 7-8 years were recruited and completed this study. All dyslexic children completed 10-weeks of visual perceptual training. The visual perceptual skills were assessed and binocular visual evoked potentials (VEP) were recorded with two different pattern stimulations initially (Baseline), 3 months after the first assessment (Evaluation I) and 6 months after first assessment (Evaluation II).

OUTCOMES AND RESULTS

A significant reduction (p = 0.021) in VEP amplitudes in the dyslexic subjects in response to 15 Hz reversal frequency at 15% contrast stimulation was found, compared with controls, prior to perceptual training. A significant correlation (p = 0.005) was found between the VEP amplitude with 15 Hz reversal frequency and the total score of Test of Visual Perceptual Skills (non-motor) - revised (TVPS-R). After training, dyslexic subjects scored higher in some of the visual perceptual tasks and these improvements persisted for 3 months. However, the VEP amplitude in the dyslexics showed no significant change after perceptual training.