Effect of stimulus contrast on simultaneous steady-state pattern reversal electroretinogram and visual evoked response

Electrophysiological Assessment of Visual Pathways in Glaucoma

Purpose.

To assess nerve conduction in visual pathways in patients with open-angle glaucoma.

Methods.

Pattern-electroretinograms (PERG) and visual-evoked potentials (VEP) were simultaneously recorded in 16 patients with open-angle glaucoma (POAG) and 15 age-matched controls. The visual stimuli were checker-board patterns (the check edges subtend 15’; the contrast was 70% and reversed at the rate of 2 reversals/s).

Results.

POAG patients showed significantly higher PERG and VEP latencies (ANOVA: P<0.01) and significantly lower amplitudes than controls; the retinocortical time (RCT: difference between VEP P100 latency and PERG P50 latency) was longer (P<0.01) in POAG than controls and the longer RCT was correlated with the reduced PERG amplitude (r:0.798, P<0.01).

Conclusions.

This suggests that POAG patients have an involvement of the innermost retinal layers and impaired nerve conduction in their visual pathways.

Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis

The pattern electroretinogram (PERG) provides an objective measure of central retinal function, and has become an important element of the author's clinical visual electrophysiological practice. The PERG contains two main components, a positivity at approximately 50ms (P50) and a larger negativity at approximately 95ms (N95). The P50 component is affected by macular dysfunction with concomitant reduction in N95. The PERG therefore complements the Ganzfeld ERG in the assessment of patients with retinal disease. In contrast, the ganglion cell origins of the N95 component allow electrophysiological evaluation of ganglion cell function both in primary disease and in dysfunction secondary to optic nerve disease, where selective loss of N95 can be observed. Both macular dysfunction and optic nerve disease can give abnormalities in the visual evoked cortical potential (VEP), and the PERG thus facilitates more meaningful VEP interpretation. This review addresses the origins and recording of the PERG, and then draws on extensive clinical data from patients with genetically determined retinal and macular dystrophies, other retinal diseases and a variety of optic nerve disorders, to present an integrated approach to diagnosis.

Neural conduction in the visual pathways in ocular hypertension and glaucoma

BACKGROUND

The aim of our work was to evaluate neural conduction in visual pathways in subjects with ocular hypertension and glaucoma.

METHODS

We assessed simultaneous recordings of pattern electroretinograms (PERG) and visual evoked potentials (VEP) in 16 subjects with ocular hypertension (OHT), in 16 subjects with primary open-angle glaucoma (POAG) and in 15 age-matched controls. The visual stimuli were checkerboard patterns (the check edges subtend 15 min of visual arc; contrast 70%) reversed at the rate of 2 reversals/s.

RESULTS

In OHT and POAG patients we found PERG and VEP latencies significantly longer than in controls. The P50-N95 PERG amplitudes were significantly reduced in OHT and POAG eyes. VEP amplitudes were significantly reduced in POAG eyes, while in OHT they were similar to controls. The retinocortical time (RCT; difference between VEP P100 latency and PERG P50 latency) was longer in POAG patients than in controls; no differences between patients with OHT and controls were observed. Moreover, we observed that in POAG the longer RCT was inversely related to the PERG amplitude.

CONCLUSION

Our results suggest that involvement of the innermost retinal layers in POAG is accompanied by slowed neural conduction in the visual pathways.

Pattern-reversal electroretinograms and visual evoked potentials in branch retinal vein occlusion

We recorded pattern electroretinograms and visual evoked potentials in a group of selected patients with unilateral uncomplicated branch retinal vein occlusion. To document the effects of preexisting risk factors, patients were divided into three groups: diabetes mellitus, hypertension with hyperlipidemia and no systemic disease. The transient and steady-state pattern electroretinogram and visual evoked potential amplitudes were significantly reduced and visual evoked potential peak times were delayed relative to the fellow eyes and age-matched normal subjects. There was a second amplitude reduction relative to the other patient groups in both the affected and fellow eyes of the diabetes mellitus group, which was indicative of an additive effect of diabetes mellitus.

Influence of simultaneous pattern-reversal electroretinogram recording on visual evoked potentials

Little is known about the influence of the presence of a gold-foil electrode on pattern-reversal visual evoked potential recording, although simultaneous pattern-reversal electroretinography has been applied in several clinical investigations. We compared the results of pattern-reversal visual evoked potentials simultaneously recorded with pattern-reversal electroretinograms with those obtained during separate pattern-reversal visual evoked potential recording in 10 normal subjects. Transient response (reversal rate, 1 Hz; check size, 30') and steady-state response (reversal rate, 5 Hz; check size, 120', 60', 30', 15' and 7.5') were analyzed under the stimulus contrast condition of 90%. Neither P100 latency in transient responses nor amplitudes in steady-state responses exhibited significant change at any check size when they were recorded separately or simultaneously with pattern-reversal electroretinograms. The results suggest that the gold-foil electrode exerts no significant influence on pattern-reversal visual evoked potentials. Simultaneous pattern-reversal electroretinogram and visual evoked potential recording is therefore confirmed to be a clinically useful method. This procedure makes the synchronous recording of both responses possible under the identical stimulus conditions.