Correlation between photopic negative response and retinal nerve fiber layer thickness and optic disc topography in glaucomatous eyes.

PURPOSE: To investigate whether there is a significant correlation between the photopic negative response (PhNR) of the electroretinogram (ERG) and retinal nerve fiber layer thickness and optic disc topography in glaucomatous eyes.

METHODS

Ninety-nine eyes of 53 patients with open-angle glaucoma (OAG) and 30 eyes of 28 normal volunteers were studied. Photopic ERGs were elicited by red stimuli (644 nm, 1600 cd/m(2)) on a blue background (470 nm, 40 cd/m(2)). The mean deviation (MD) of the visual field was obtained by static visual field analyses. The topography of the optic nerve head was determined by confocal scanning laser ophthalmoscopy. The retinal nerve fiber layer thickness (RNFLT) around the optic nerve head was measured with a scanning laser polarimeter.

RESULTS

The amplitude of the PhNR and the PhNR/b-wave ratio decreased with an increase in visual field defects. The logarithmic values of the PhNR amplitude and PhNR/b-wave amplitude ratio were significantly correlated with the MD better than the linear values. The PhNR amplitude and PhNR/b-wave amplitude ratio were significantly correlated with the RNFLT and the rim area of the optic disc and with the cup/disc area ratio. These correlations were higher when expressed linearly than when stated logarithmically. The sensitivity and specificity were 77% and 90% for the PhNR amplitude and 70% and 87% for the PhNR/b-wave amplitude ratio when the optimal cutoff values were used. Although the a-wave amplitude correlated with the MD, the a-wave amplitudes of most of the patients fell within the normal range. The correlation between the b-wave amplitude and MD was not significant.

CONCLUSIONS

The PhNR amplitudes correlate with the decrease in function and morphology of retinal neurons in eyes with OAG. The linear relationship between the PhNR and the structural parameters indicates that inner retinal function declines proportionately with neural loss in eyes with glaucoma.