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Antonello Fadda, Antonio Di Renzo, Francesco Martelli, Dario Marangoni, Anna Paola Batocchi, Daniela Giannini, Benedetto Falsini; Habituation of the Ganglion Cell Response to Sustained Pattern Stimulation: Reduced by Multiple Sclerosis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5734.
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© ARVO (1962-2015); The Authors (2016-present)
The electroretinogram in response to sustained pattern stimulation (PERG) shows in normal subjects adaptive changes (habituation) which have been interpreted as reflecting buffering mechanisms in the glial cells of inner retina, adjusting sensitivity and gain of retinal ganglion cells (RGC).The aim of this study was to compare habituation of RGC of normal subjects with that of patients with multiple sclerosis (MS) and no optic neuritis.
Ten MS patients and six age matched control subjects were included in the study. PERG was elicited by a sinusoidal grating of 1.7 cycles/degree spatial frequency and 90% contrast (mean luminance: 35 cd/m2), modulated in counterphase at 7.5 Hz (15 reversals/second). Stimulus was presented continuously over 3 minutes and response recorded as a continuous sequence of 20 synchronous averages, each one spanning over a 60 cycles time (8 s average duration). A three point moving average was finally used to improve S/N ratio, with only a limited effect on time resolution. Amplitude and phase of the response 2nd harmonic were computed for every block, producing the time series needed to study the adaptive changes.
Habituation changes were evaluated for every subject of the two groups using a linear model on normalized amplitude data. The first order differential model used in previous studies was not suitable for MS patient records, due to reduced amplitude levels. Final measurements are expressed as relative amplitude reduction (delta%) over the full examination time. In normal subjects PERG amplitude during sustained stimulation declined progressively and then reached a plateau (delta=22.9% SE=3.5%). In patients, the amplitude declined from the initial value of a smaller amount (delta=11.4% SE=3.6%), but this was still a detectable trend (p<0.02), and the difference with the control value was found to be significant (p<0.05).
The results show reduced RGC habituation in MS patients, suggesting an abnormal gain and sensitivity control in the inner retina even in absence of clinical optic neuritis.
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