The multifocal ERG in open angle glaucoma--a comparison of high and low contrast recordings in high- and low-tension open angle glaucoma.

High and low contrast multifocal ERG (MF-ERG) recordings were obtained from the right eyes of 24 patients with OAG (high-tension OAG: n=16, low-tension OAG: n=8) and compaired to those recorded from 18 healthy volunteers. High contrast MF-ERG recordings were obtained at a mean luminance of 100 cd/m2 with a contrast of 99%, while low contrast MF-ERGs were obtained at a mean luminance of 100 cd/m2 with a contrast of 50%. During MF-ERG recordings the central 50 degrees of the retina were stimulated by 103 hexagons. A MF-ERG recording lasted eight minutes, a M-sequence of 2(15) was used. The first order response component (KI, mean focal flash response) and the first and second slice of the second order response component (mean focal two flash interaction of flashes one, KII. 1, or two, KII.2, base intervals apart) were analyzed for group differences. Group differences were found mainly in latency measures. These included a delay in the central response average of the first positive peak, P1, in KII.2 (p < or = 0.05) in OAG high contrast recordings. Low contrast recordings showed a significant delay in the central response average of the first negative peak, Nl, in KII.2 as well as in the peripheral response average of N1 in KI and of P1 in KII.2 (p<0.05) in OAG. Amplitudes were only affected significantly in KI of the low contrast recordings. Here the amplitude N1P1 was significantly higher in high tension (n=16) than in low tension (n=8) OAG patients. However, an overlap in all of the response parameters tested allowed only group differences to be characterized. Under these stimulus conditions, neither high contrast recordings nor low contrast recordings seem sensitive enough to reliably recognize early glaucomatous retinal dysfunction.