Decreased nasal-temporal asymmetry of the second-order kernel response of multifocal electroretinograms in eyes with normal-tension glaucoma.

PURPOSE: To determine whether multifocal electroretinograms (mfERGs) can provide an index for identification of glaucomatous optic neuropathy in patients with normal-tension glaucoma (NTG).

METHODS: mfERGs were recorded in 30 normal volunteers (30 eyes) and 20 patients (20 eyes) with normal-tension glaucoma (NTG). Visual field examinations were performed with a Humphrey field analyzer, and all NTG patients had unilateral hemifield defects. The mfERGs were elicited by a binary m-sequence of flashes from 37 hexagonal elements that subtended an overall visual angle of 50 degrees x 40 degrees. The mfERGs were summed and analyzed for predetermined retinal loci. These mfERGs were compared with the perimetric findings of the corresponding visual fields.

RESULTS: In normal volunteers, the amplitude of the second-order kernel within the central 5 degrees of the nasal hemisphere was significantly smaller than in that of the temporal hemisphere (Wilcoxon signed-rank test, P = 0.0001). In NTG patients, this asymmetry of the two hemispheres was reduced or not present. The ratio of the amplitude of the mfERGs from the nasal and temporal hemispheres (N/T amplitude ratio) in normal control volunteers was significantly different from that of NTG patients with a hemifield defect (analysis of variance, P = 0.0001). When the cutoff value for the N/T amplitude ratio was set at 0.83 for discriminating glaucomatous eyes from normal eyes, the sensitivity was 65.0% with a specificity of 96.7%. The area under the receiver-operating characteristic curve of the N/T amplitude ratio was 0.86. The N/T amplitude ratio and the visual field indices were significantly correlated.

CONCLUSION: A decrease in the nasal-temporal asymmetry in the amplitude of the second-order kernel responses within the central 5 degrees of glaucoma patients' eyes indicated a dysfunction of the inner retinal layers, including of the retinal ganglion cells.