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.