Reduced habituation of the retinal ganglion cell response to sustained pattern stimulation in multiple sclerosis patients

OBJECTIVE: Sustained pattern stimulation in normal subjects induces adaptive changes in pattern electroretinogram (PERG), an effect that has been interpreted as a response of glial cells and retinal ganglion cells (RGC). The aim of this study was to compare the effect in normal subjects and in multiple sclerosis patients without previous optic neuritis. METHODS: PERGs were elicited by a 7.5 Hz pattern stimulus, presented continuously over 152 s. Response cycles were averaged in 20 packets of 60 events each and amplitude and phase of the 2nd harmonic response was measured. Adaptive changes are expressed as amplitude reduction over the full examination time. RESULTS: In normal subjects PERG amplitude declined progressively to a plateau (dA=-0.46 μV, SE=0.09 μV); in patients the effect size was severely reduced (dA=-0.20 μV, SE=0.04 μV). No significant difference was found in mean amplitude. CONCLUSIONS: The results show reduced RGC habituation in patients, suggesting an abnormal gain and sensitivity control in the inner retina, even in absence of clinical optic neuritis. Recent findings in astrocyte biology and indications drawn from a mathematical model point to a key role of glial cells in this process. SIGNIFICANCE: The proposed methodology may have implications in the assessment of MS patients and in understanding the pathophysiology of neurological and retinal disorders.