To study the ability and sensitivity of the slow stimulation multifocal ERG (mfERG) to detect glaucomatous damage.Methods:
Right eyes of 20 patients with normal-tension glaucoma (NTG), 15 patients with high-tension glaucoma (HTG) and 15 healthy volunteers underwent testing with the mfERG (VERIS 4.1TM). The central 50 degrees of the retina were stimulated by 103 hexagons (m-sequence: 213-1, Lmax: 100 cd/m2, Lmin: 1 cd/m2, background: 50 cd/m2). Each m-sequence step was followed by 3 black frames (Lmax: < 1 cd/m2). Five response averages of the first order response component (KI) were analyzed: the central 7.5 degrees and the 4 adjoining quadrants. The amplitudes from the first minimum, N1, to the first maximum, P1, and from P1 to the second minimum, N2, were analyzed as well as the latencies of N1, P1, N2 and the latencies of 3 multifocal oscillatory potentials (mfOPs) with their maxima at about 73, 80 and 85 ms.Results:
For each parameter the percentage of deviation from the mean of the control group was calculated. These values were then added for each individual to form a deviation index (DI). Seventeen patients (85.0%) with NTG and 3 patients (20.0%) with HTG showed a DI outside the normal range. The major changes were observed in the mfOPs of the NTG patients. MfOPs were then selectively filtered at 100-300 Hz and their scalar product was analyzed over an epoch of 68-105 ms. This confirmed that mfOPs differed significantly from the control in the central 7.5° and, for NTG, in the nasal field. With a logistic regression analysis the mfOPs had a sensitivity to differentiate 85% of the NTG patients and 73% of the HTG patients from normal.Conclusions:
Under these conditions, the slow-stimulated mfERG can detect glaucomatous dysfunction in NTG (85.0%). The differences observed between NTG and HTG are in support of a different underlying pathomechanism.