Electrophysiology in neuro-ophthalmology

The diagnostic accuracy of photopic negative responses evoked by broadband and chromatic stimuli in a clinically heterogeneous population

PURPOSE

To compare the diagnostic accuracy of the photopic negative response (PhNR) elicited by red-blue (RB) and white-white (WW) stimuli, for detection of retinal ganglion cell (RGC) dysfunction in a heterogeneous clinical cohort.

METHODS

Adults referred for electrophysiological investigations were recruited consecutively for this single-centre, prospective, paired diagnostic accuracy study. PhNRs were recorded to red flashes (1.5 cd·s·m-2) on a blue background (10 cd·m-2) and to white flashes on a white background (the latter being the ISCEV standard LA 3 stimulus). PhNR results were compared with a reference test battery assessing RGC/optic nerve structure and function including optical coherence tomography (OCT) retinal nerve fibre layer thickness and mean RGC volume measurements, fundus photography, pattern electroretinography and visual evoked potentials. Primary outcome measures were differences in sensitivity and specificity of the two PhNR methods.

RESULTS

Two hundred and forty-three participants were initially enrolled, with 200 (median age 54; range 18-95; female 65%) meeting inclusion criteria. Sensitivity was 53% (95% confidence intervals [CI] 39% to 68%) and 62% (95% CI 48% to 76%), for WW and RB PhNRs, respectively. Specificity was 80% (95% CI 74% to 86%) and 78% (95% CI 72% to 85%), respectively. There was a statistically significant difference between sensitivities (p = 0.046) but not specificities (p = 0.08) of the two methods. Receiver operator characteristic (ROC) area under the curve (AUC) values were 0.73 for WW and 0.74 for RB PhNRs.

CONCLUSION

PhNRs to red flashes on a blue background may be more sensitive than white-on-white stimuli, but there is no significant difference between specificities. This study highlights the value and potential convenience of using white-on-white stimuli, already used widely for routine ERG assessment.

Morphological and Functional Assessment of the Optic Nerve Head and Retinal Ganglion Cells in Dry vs Chronically Treated Wet Age-Related Macular Degeneration

Purpose

The aim of the study comprised the anatomical and functional assessment of the optic nerves and macular ganglion cells in the population of patients with unilateral wet age-related macular degeneration (wAMD) and comparison of its results to those obtained from the fellow eye with non-advanced dry age-related macular degeneration (dAMD). Furthermore, we aimed to determine if the number of administered injections contributed to the potential differences between the examined eyes.

Methods

The study was based on 104 eyes of 52 patients in a cross-sectional study. The eyes with chronically treated wAMD were the main subject of the study, while fellow eyes affected with non-advanced dAMD served as the control group. Primary morphological outcomes comprised differences in peripapillary retinal nerve fiber layer (RNFL) and GCC layers between the studied groups (treated and control). In turn, primary functional outcomes included differences in implicit times and amplitudes of the P100 wave of pattern visual evoked potentials (PVEP) and N95 wave of pattern electroretinogram (PERG) between treated and control groups.

Results

We did not find any differences in total RNFL thickness between wAMD and dAMD groups. The number of injections only affected the RNFL in the nasal quadrant of the optic disc (p = 0.023). We did not find any differences regarding GCL thickness in both groups. In the study group, a longer implicit time of the P100 of PVEP (p = 0.014) and a shorter amplitude of the P50-N95 wave of PERG (p = 0.005) were detected. The total number of injections had no significant effect on these two values.

Conclusion

We detected worse functional parameters of the optic nerve and retinal ganglion cells in eyes with wAMD, with lack of significant differences in anatomical (RNFL, GCL) parameters compared to the control group. However, the number of injections did not contribute to the differences found.