The Relationship Between the Photopic Negative Response and Retinal Ganglion Cell Topography.

Purpose: To assess the topographic relationship between the photopic negative response (PhNR) and retinal ganglion cell distribution in healthy individuals. Method: Data was recorded from 16 healthy participants. The amplitude of PhNRs obtained in response to focal long duration (250 ms) and brief flash (5 ms), red (660 nm) on blue (469 nm) stimuli of increasing size (5° - full field) were measured. The number of retinal ganglion cell receptive fields (RGCf) in each stimulus area was established from the literature and regression analysis used to determine the relationships between: PhNR amplitude and number of RGCfs stimulated, PhNR density and the RGCf density and response per RGCf as a function of eccentricity. Results: The overall amplitude of the PhNR increased with stimulus size and the response density declined from ∼0.1 µV/deg in the macular region to ∼0.003 µV/deg approximately 45° from the fovea. Contrary to expectations, the relationship between the PhNR and number of RGCf was nonlinear, the response from more eccentric neurons being about three times greater than those in the macular region. Conclusions: Although the amplitude of the PhNR broadly maps on to the topographic distribution of RGCf the increase in PhNR amplitude with increasing eccentricity is only partly explained by RGCf numbers. Increases in the PhNR amplitude may be due to topographic variations in the contributions from other non-RGC neurons, as well as eccentricity-related morphologic and physiologic differences in RGCs.

Electrophysiological ON and OFF Responses in Autosomal Dominant Optic Atrophy.

PURPOSE: To assess the effect of autosomal dominant optic atrophy (ADOA) on ON and OFF retinal ganglion cell (RGC) function by evaluating the ON and OFF components of the photopic negative response (PhNR). METHODS: Twelve participants from six families with OPA1 ADOA and 16 age-matched controls were recruited. Electrophysiological assessment involved pattern ERGs (PERGs), focal (20°) and full-field long-duration (250 ms) flash ERGs using a red light-emitting diode flash on a rod-saturating blue background, and full-field brief (300 µs) xenon flash ERGs using a red filter over a continuous rod saturating blue background. Amplitudes and implicit times of the ERG components were analyzed and the diagnostic potential of each electrophysiological technique was determined by generating receiver operating characteristic (ROC) curves. RESULTS: Mean amplitudes of the N95 and all PhNRs, except the full-field PhNRON, were significantly reduced in participants with ADOA (P < 0.01). Subtraction of the group-averaged focal ERG of ADOA participants from that of controls showed an equal loss in the focal PhNRON and PhNROFF components, whereas in the full-field ERG the loss in the PhNROFF was greater than that in the PhNRON component. The areas under the ROC curve (AUC) for the focal PhNRON (0.92), focal PhNROFF (0.95), and full-field PhNROFF (0.83), were not significantly different from that of the PERG N95 (0.99). CONCLUSIONS: In patients with ADOA, the PhNRON and PhNROFF components are nearly symmetrically reduced in the long-duration ERG, suggesting that ON- and OFF-RGC pathways may be equally affected.