Considerations for paediatric electrophysiology
Authors: Thompson Dorothy A. 
Published: January 2025

Visual electrophysiology is a powerful, objective test of function and especially valuable for children and others who are unable to communicate what they can see. This talk will explore by clinic example, acceptable, robust tests for alert young children that are diagnostically accurate.

Some considerations:

Visual pathway maturity – uncomplicated delayed visual maturation does not delay the timing of electrophysiology and that fundal signs may not be as apparent as for adults, such as pigmentary changes or optic atrophy take time to appear. Children may not present with classical symptoms or signs of a specific condition. Most referrals are to investigate unexplained poor behavioural vision.

Dynamic protocols – adapting test order according to the findings in the moment are most efficient. The simultaneous recording of ERG and VEP are the base of the diagnostic decision tree. For nystagmus published studies estimate 55‐75% of cases have a sensory defect of the anterior visual pathway, balanced 50% retinal conditions and 50% optic nerve and chiasm – distinguished by the combination of ERG and VEP.

Skin electrode flash ERG protocol – skin electrodes are easier to apply and more acceptable than corneal electrodes for young children. An adapted skin flash ERG can provide similar diagnostic accuracy to ISCEV ffERG by incorporating some elements of extended ERG protocols to help separate rod and cone system, using their relative chromatic sensitivities.

Simultaneous acquisition of skin ERG with flash VEPs – technically ensures adequate monocular retinal stimulation or occlusion in a restless child and maximises information capture in a short chair time. We aim for 30 minutes.

For VEPs ‘more’ than Standard has better diagnostic accuracy for children.

More electrodes – we advocate a trans‐occipital multi‐channel array in all children with two midline electrodes. The single Oz recommended by ISCEV for adult pre‐chiasmic application can misclassify ~4% of children as abnormal, avoided by adding an inion electrode.

More modes of stimulation – pattern reversal, pattern onset and flash stimulation each produce VEPs that provide distinct and complementary localisation of visual pathway dysfunction. These VEPs can distinguish hemisphere and chiasmal pathology when a young child may not be able to comply with hemifield stimulation or visual field assessment.

More check widths – the spatial sensitivity of the visual system and shape of the VEP changes throughout life. Pattern VEPs can monitor visual pathway maturation and estimate vision levels qualitatively. Larger checks may be more susceptible to inflammation and smaller checks to optic atrophy. The pattern reversal VEP is physiologically analogous to a clinical measure of low contrast visual ability rather than high contrast acuity. The sweep VEP can provide a spatial frequency threshold but it is highly dependent on the condition, less able to predict vision in cases of optic atrophy, it is an adjunctive rather than diagnostic test.

Biomarkers – adapted visual electrophysiology can describe the natural history of rare conditions in children when adult protocols may not be tolerated. This offers potential objective biomarkers for stratification and outcome measures for clinical trials involving children.