Brief report: harmonic analysis of the 30 Hz flicker ERG in early-stage diabetic retinopathy.

PURPOSE

To determine if harmonic components of the 30 Hz flicker ERG are useful for detecting neural dysfunction in diabetics who have mild or no non-proliferative diabetic retinopathy (NPDR).

METHODS

Previously reported light-adapted flicker ERG data recorded from 20 diabetics who had no clinically-apparent retinopathy (NDR), 20 who had mild NPDR (MDR), and 20 non-diabetic controls were reanalyzed. From this dataset, the amplitude and phase of the 31.25 Hz flicker ERG fundamental and second harmonic were extracted. The 62.5 Hz flicker ERG fundamental was also extracted. Similar responses were also acquired prospectively from 10 controls, 5 NDR, and 5 MDR subjects, comprising a second dataset.

RESULTS

Analysis of variance indicated that both diabetic groups had normal amplitudes elicited by the 31.25 Hz stimulus (fundamental and second harmonic), whereas the 62.5 Hz amplitude was reduced significantly in both diabetic groups. This pattern was found in both the retrospective and prospective analyses.

CONCLUSIONS

The second harmonic of the 31.25 Hz flicker response (equivalent to 62.5 Hz) was normal in early-stage DR, whereas the response to 62.5 Hz flicker stimuli was abnormal. The second harmonic of the ISCEV standard 30 Hz flicker ERG does not appear to be a useful indicator of neural dysfunction in early DR.