Electrophysiological assessment of paediatric visual function in conditions of raised intracranial pressure

Marmoy, Oliver Rajesh (2024) Electrophysiological assessment of paediatric visual function in conditions of raised intracranial pressure. Doctoral thesis (DClinSci), Manchester Metropolitan University.

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Abstract

Measuring visual function in paediatric practice can be challenging. Children can be lively and spirited, yet this sometimes results in behaviours that are difficult to channel into enthusiasm or focus for performing clinical tests. This is often a result of conventional clinical measurements tending to be unexciting, demanding of attention or requiring of high concentration levels. This is particularly problematic when monitoring vision, which is crucial to diagnose sight threatening conditions such as raised intracranial pressure (rICP). In rICP, elevated intracranial pressure causes impairment of the optic nerve and retinal ganglion cell (RGCs) function. Consequently, visual monitoring is critical to prevent irreversible sight loss and clinical morbidity in rICP, yet existing techniques are often subjective, insensitive or not child-friendly. This thesis investigates how electrophysiological measurements, specifically the photopic negative response (PhNR), can be applied in the paediatric setting for measuring visual function in rICP. The major contributions of this thesis include an empirical understanding of how stimulus and recording characteristics can influence the PhNR, specifically in relation to temporal frequency, background luminance, electrode type and measurement approach. These findings are used to provide a method for recording the PhNR in children through development of a modified protocol without loss of diagnostic efficacy. When this modified PhNR protocol was applied in children, including those with rICP, it was found that that the PhNR shows enhanced sensitivity in relation to the degree of optic disc oedema observed in rICP. This is hypothesised to reflect hyperexcitability of RGCs and may reflect a potential compensatory mechanism arising within the proximal retina. Future work in this area in the form of longitudinal studies are needed to establish the time-course and mechanisms of this change to understand their clinical importance. As enhanced RGC sensitivity has been associated with photophobia and migraine, these findings prompt further study associating these features with those changes observed in this study to identify any causative mechanisms which may exist.