Relationship Between Multifocal ERG and VEP Components in Retinitis Pigmentosa

Abstract

Abstract: : Purpose: To determine the impact of the loss of retinal function on the visually–evoked cortical activity in retinitis pigmentosa (RP), by evaluating the relationship between multifocal ERG (MERG) and multifocal VEP (MVEP) components. Methods: MERGs and MVEPs were recorded from 10 typical RP patients (20 eyes, visual acuity > 20/30, Goldmann visual field by V/4e target: 30–50 degrees, non–recordable Ganzfeld rod–mediated ERGs and severely reduced cone–mediated ERGs, mean age: 35.4±3.2 years, range: 18–56) as well as from eight age–matched controls, in response to 61 and 60 M–stimuli presented to the central 20 degrees of the visual field. Response amplitude density (nV/deg²) and time–to–peak (ms) of the N1–P1–N2 components of MERG first order binary kernels and MVEP second order binary kernels were measured. Ring analysis, matched for MERG and MVEP stimuli, was performed every five retinal eccentricities between fovea (0–2.5 degrees) and mid–periphery (15–20 degrees). Results: In RP eyes, independently of retinal eccentricity, MERG N1 response densities were positively correlated (Pearson’s r = 0.68, p < 0.05) with corresponding MVEP P1 densities. Similarly, MERG P1 times–to–peak were positively correlated (r = 0.6, p < 0.05) with corresponding MVEP P1 times–to–peak. Both MERG and MVEP P1 response density losses and delays showed a topographic relationship with perimetric losses measured at corresponding retinal eccentricities. Conclusions:The results indicate that, in RP eyes, losses in N1 response density as well as delays in P1 time–to–peak of the MERG most accurately predict corresponding losses in the MVEP main positive component. Since MERG N1 is thought to be generated by photoreceptors and off bipolar cells¹, these data suggest that functional losses of these neural generators have a major impact on the characteristics of the corresponding cortical responses. ¹Hood, Prog Ret Res 2000, 19: 607–646

Keywords: electroretinography: clinical • photoreceptors: visual performance • visual fields