Correlation between ERG and morphometric parameters of optic nerve head and nerve fiber layer

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Purpose : To determine the relationship between the photopic negative response (PhNR) of the focal electoretinogram (ERG) and the structural parameters of the inner retina and optic nerve head in glaucoma. Methods : Sixty-one eyes of 61 patients with open angle glaucoma (OAG), 13 eyes of 13 patients who were classified as glaucoma suspects, and 30 eyes of 30 normal subjects were studied. The focal ERGs were elicited by a 15° circular white stimulus on a white background centered on the fovea. The focal ERGs were also elicited by half of an annulus placed above or below the macula. The diameter of the inner border of the annulus was 15° and that of the outer border was 30°. The structure of the optic nerve head and retinal nerve fiber layer thickness (RNFLT) were evaluated by scanning laser ophthalmocopy and laser scanning polarimetry, respectively. Results : The amplitudes of the focal PhNRs and the ratio of the focal PhNR/b-wave amplitude were linearly correlated with the corresponding RNFLT in the superior/temporal and inferior/temporal regions (r=0.43 to 0.47 ; P<0.0001) but not in the temporal region. The focal PhNR amplitude and focal PhNR/b-wave amplitude ratio were also linearly and significantly correlated with the corresponding rim areas and cup/disc area ratio (r=0.38 to 0.50, P<0.0001). Conclusions : These results strongly suggest that the anatomical losses of retinal neurons in local areas of the retina or optic nerve head are a cause of the reduction in the amplitude of the focal PhNR in OAG..