Correlation between Photopic Negative Response of Focal Electroretinograms and Local Loss of Retinal Neurons in Glaucoma

Abstract

Purpose: To determine the relationship between the photopic negative response of the focal electroretinogram 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, 13 eyes of 13 patients who were classified as glaucoma suspects, and 30 eyes of 30 normal subjects were studied. The focal electroretinograms were elicited by a 15° circular white stimulus on a white background centered on the fovea. The focal electroretinograms 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 were evaluated by scanning laser ophthalmoscopy and laser scanning polarimetry, respectively.

Results: The amplitudes of the focal photopic negative responses and the ratio of the focal photopic negative response/b-wave amplitude were linearly correlated with the corresponding retinal nerve fiber layer thickness 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 photopic negative response amplitude and focal photopic negative response/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 photopic negative response in open angle glaucoma.

KEYWORDS::

• Electroretinogram
• Focal electroretinogram
• Glaucoma
• Photopic negative response
• Retinal nerve fiber layer

ACKNOWLEDGMENTS

This study was supported by a Grant-in-Aid from Ministry of Education, Culture Science and Technology in Japan No. 20592056 (SM) and 21791707 (HM); Grant from Keiryokai Research Foundation No. 102 (SM and KT); Grant from The Imai Memorial Fund for Research (SM). The authors especially thank Mrs. Aki Kaneko and Yoshiharu Toba for their excellent help in collecting the data.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.