Use of a handheld electrophysiology device (RETeval, LKC) to identify visual pathway decussation defects

Keeling, Eloise, Carter, Perry, Shawkat, Fatima, Lee, Helena and Self, Jay (2023) Use of a handheld electrophysiology device (RETeval, LKC) to identify visual pathway decussation defects. Investigative Ophthalmology & Visual Science, 64, [5325]. (In Press)

Abstract

Purpose : electrodiagnostic testing (EDTs) require large equipment and trained clinical scientists so are restricted to specialist centres, and often have long waiting lists. Pattern and flash visual evoked potentials (fVEP) have been utilised in the assessment of visual pathway integrity, including chiasmal anomalies in albinism. In this qualitative clinical study, we assess the potential of the handheld RETeval to screen for excess nerve decussation and other post-chiasmal defects.

Methods : 18 patients with suspected albinism or retro-chiasmal lesions (aged 0-15yrs, mean 5) were selected from those undergoing routine EDTs at a regional referral centre. Standard paediatric EDTs were performed, followed by fVEP using the RETeval. Control data was collected from 12 volunteers (aged 26-54yrs, mean 32). Right and left occipital electrodes were placed midway between Oz (10-20 system) and either ear. The ground electrode was placed at Fz. FVEPs of 3cd.s/m2 were recorded from 10 brief (<5ms) 1Hz flashes. The left occipital VEP waveform was subtracted from that of the right occiput, creating a single channel response for each eye separately. RETeval data was compared to results obtained from the standard paediatric protocol using a photic stimulator (Grass PS 22). Pearson’s correlation was used to calculate the extent of asymmetry, where a value of -1 showed complete asymmetry whilst a value of +1 showed absolute symmetry in occipital VEP distribution. Data between controls and patients were compared using a Mann-Whitney U test.

Results : FVEP testing using both the standard protocol and the RETeval identified asymmetry in 11 patients with suspected albinism. The Pearsons correlate of the albinism cohort (-0.504 ± 0.208) was compared to the control data (0.184 ± 0.339) and a Mann-Whitney U test showed a significant difference between the two groups (p<0.001). This demonstrates the effectiveness of the RETeval in detecting crossed asymmetry secondary to excessive nerve decussation in albinism. The RETeval also detected 7 cases of left and right retro-chiasmal lesions that showed an uncrossed asymmetry.

Conclusions : this study adds to the growing body of work investigating the use of the handheld RETeval device for prioritising patients waiting for in-depth EDTs. This data shows the RETeval has the potential to be used as a screening tool for the detection of chiasmal and retro-chiasmal anomalies.

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Contributors

Author: Eloise Keeling

Author: Helena Lee

Author: Jay Self

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