Lack of habituation in the light adapted flicker electroretinogram of normal subjects: A comparison with pattern electroretinogram

Objective: Sustained pattern stimulation (SPS) induces habituation in the normal pattern electroretinogram (PERG). In this study, the authors evaluated whether sustained flicker stimulation (SFS) induces habituation in the normal flicker ERG (FERG). Methods: FERGs were elicited in normal volunteers by an 8 Hz flicker stimulus, presented continuously over 3 min after 20 min of light adaptation. One stimulus temporal period was sampled and averaged in packets (n = 20) of 60 events, each of 8 s duration. Amplitudes and phases of the response 1st and 2nd harmonics (1F and 2F, respectively) were measured. FERG results were compared with those obtained by recording PERGs with a similar SPS paradigm. Results: During SFS, FERG 2F showed a modest increase in amplitude (about 25%, p < 0.05). No changes were observed for the 1F amplitude and for the phase of both components. In contrast, PERG amplitude showed SPS-induced habituation, described by an exponential decay with a time constant of similar to 20 s. Conclusions: The normal FERG, unlike PERG, does not show habituation, suggesting that the adaptive changes of retinal neurons underlying FERG are different from those of PERG generators. Significance: Our findings may have implications for diagnosis and/or pathophysiology of retinal disorders involving the inner retina. (C) 2009 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology.