The photopic negative response in idiopathic intracranial hypertension

Purpose: To evaluate the photopic negative response (PhNR) as an index of retinal ganglion cell (RGC) function in idiopathic intracranial hypertension (IIH). Methods: Amplitude and implicit time of the PhNR, as elicited by full-field, brief-luminance flashes was measures in IIH (n=10) and visually-normal control (n=15)subjects. Visual function was assessed in IIH subjects using standard automated perimetry mean deviation (SAP-MD) scores. Optic nerve structure was evaluated using the Frisén papilledema grading scale (FPG). Macula ganglion cell complex volume (GCCV) was extracted from optical coherence tomography images to assess RGC loss. Results: Median PhNR amplitude was significantly lower in IIH subjects compared with control subjects (p=0.015, Mann-Whitney Rank Sum (MW)), but implicit time was similar (p=0.54, MW). In IIH subjects, PhNR amplitude and SAP-MD were correlated (Pearson’s r=0.78, p=0.008). GCCV was correlated with both SAP-MD (r=0.72, p=0.019) and PhNR amplitude (r=0.77, p=0.009). Multivariate linear regression models demonstrated that the correlation between GCCV and PhNR amplitude was improved by accounting for FPG in the model (r=0.94, p <0.0001), but the correlation between GCCV and SAP-MD was not (r=0.74, p =0.009). Conclusions: PhNR amplitude, which can be decreased in IIH subjects, correlates well with a clinical measure of visual function (SAP-MD). In multivariate models it correlated with both an imaging measure of chronic ganglion cell injury (GCCV) and a clinical measure of acute optic nerve head pathology (FPG). Further studies are needed to determine the clinical utility of PhNR as a marker for diagnosis and monitoring of IIH.