Purpose
To establish the relationships between measures of visual function (standard automated perimetry (SAP)), ganglion cell function (the photopic negative response (PhNR)), ganglion cell structure and optic nerve structure in idiopathic intracranial hypertension (IIH).
Methods
Visual function was assessed using SAP mean deviation (SAP-MD) scores in 10 subjects with IIH (3 untreated, 4 active, 3 treated). The PhNR of the photopic full-field, brief flash electroretinogram, was recorded using standard stimulation and recording techniques. Ganglion cell structure was assessed using ganglion cell complex volume (GCCV) in a 3mm diameter region centered on the macula, which was semi-automatically segmented from OCT B-scans (Spectralis). Optic nerve structure was categorized according to Frisén papilledema grading scale (FPG). Associations within and between functional markers (SAP-MD, PhNR) and structural markers (GCCV, FPG) were studied with multiple linear regression (LR).
Results
Log PhNR amplitude and SAP-MD were modestly correlated (Pearson correlation, r = 0.78, p= 0.008, LR). GCCV and FPG were not associated (p=0.10, mann-whitney rank sum). SAP-MD was associated with GCCV (r=0.72, p=0.019, LR). Addition of FPG did not improve the LR model for SAP-MD. Log PhNR amplitude was also associated with GCCV (r=0.77, p=0.009, LR). Addition of FPG improved the LR model for PhNR (r=0.94, p<0.0001, p(GCCV)<0.0001, p(FPG)=0.003, LR).
Conclusions
Though visual and ganglion cell functional markers are modestly correlated, we find their individual correlations with structural markers to differ. Both SAP-MD and PhNR are related to ganglion cell atrophy, but only PhNR is also associated with degree of acute optic nerve pathology. The observation that high-grade papilledema is associated with PhNR decrease but not SAP-MD severity supports literature implicating PhNR association with pre-perimetric optic nerve injury. Further studies are needed to determine the clinical utility of PhNR as a marker for diagnosis and monitoring of IIH.