Abstract
Abstract: :
Purpose: 1. To evaluate the electrophysiologic function in glaucoma by using a new protocol of the multifocal electroretinogram (mf–ERG) that emphasizes response contributions from ganglion cell fibers (optic nerve head component (ONHC)). 2. To compare glaucomatous losses in the ONHC with those estimated through inter–ocular comparison of the multifocal visual evoked potentials (mf–VEP). Methods:mfERGs and mfVEPs of 26 individuals with glaucoma and 26 normal subjects were recorded and analysed with the VERIS 5.1 multifocal recording system. Stimulation: The special, ganglion cell response enhancing protocol consisted of multifocal flash stimuli interleaved with two global flashes presented 13.3 ms and 40 ms after each multifocal frame. The intensity of both multifocal and global flashes was 2.7 cd·s/m^2. The stimulus array consisted of 103 scaled hexagons. The recording time was 9 minutes per each eye. Pupils were dilated. The mfVEP stimulus consisted of a 60–sector dartboard grid, with each sector containing a contrast reversing check pattern. The mean stimulus luminance was 200 cd/m^2 viewed through a natural pupil. All multifocal stimulus arrays subtended ca. 45 degrees. The net recording time was 14 minutes per eye. Analysis: The effect induced by the focal flashes on the second one of the following global flashes contains the most prominent ONHC and was thus used for the evaluation of the mfERG data. Inter–ocular differences in focal VEP amplitude ratios were evaluated against those due to the noise contamination in each record.Results:In advanced glaucoma the ONHC was mostly extinct. In early glaucoma areas with a visibly reduced ONHC generally matched but exceeded areas with local sensitivity changes seen in visual field by standard automatic achromatic perimetry. This suggests a far more undetected advanced damage to the ganglion cells in glaucoma. While large local inter–ocular differences were easily detected with the mfVEP technique, homonomous bilateral damage could not easily be distinguished from local signal reduction due to the convoluted cortical anatomy. Conclusions:Our data suggest that in glaucoma, where the presentation is commonly bilateral, the ONHC protocol of the mfERG provides a better topographic evaluation than the inter–ocular mfVEP analysis. While a larger scale evaluation is needed, the study suggests that the ONHC analysis may outperform standard achromatic perimetry in sensitivity and reproducibility. Supported by NIH grant EY06861, FIS 02/0926 and The Smith–Kettlewell Eye Research Foundation
Keywords: electroretinography: clinical • electrophysiology: clinical • perimetry