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Abstract #11936 Published in IGR 7-1
Habituation of retinal ganglion cell activity in response to steady state pattern visual stimuli in normal subjects
Porciatti V; Sorokac N; Buchser WInvestigative Ophthalmology and Visual Science 2005; 46: 1296-1302
PURPOSE: To evaluate autoregulatory changes of retinal ganglion cell (RGC) activity, as measured by the pattern electroretinogram (PERG), when the eye is exposed to a steady state presentation of stimuli that maximize PERG amplitude and blood flow. METHODS: The PERG was recorded from both eyes of 14 normal subjects in response to steady state presentation (4 minutes) of contrast-reversing (16.28/s) gratings (1.6 cyc/deg) with different contrast (12%-99%) and mean luminance (40-1.3 cd/m2 ). One temporal period of the stimulus (122.8 ms) was sampled and averaged in packets of 50 sweeps ( approximately 15 seconds each). PERG amplitude and phase were evaluated by Discrete Fourier Transform and displayed as a function of time. Data were fitted with an exponential decay function to evaluate PERG changes with time. RESULTS: For patterns of 99% contrast, the PERG amplitude progressively decreased with time until reaching a plateau approximately 30% lower than the initial amplitude after approximately 2 minutes (habituation). The ratio between initial and plateau amplitude did not change by reducing the stimulus luminance by 1 log unit. However, reducing contrast decreased amplitude habituation. The habituation was abolished at 25% contrast. CONCLUSIONS: Decrease of PERG amplitude with time is consistent with a slow adaptive change of RGC activity in response to high-contrast, steady state stimuli. The authors propose that the initial amplitude represents an index of RGC activity, and the plateau amplitude represents a dynamic equilibrium between RGC activity and the available energy supply. These results are relevant for a better understanding of glaucomatous optic neuropathy.
Dr. Porciatti, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Florida, USA. vporciatti@med.miami.edu
Classification:
6.7 Electro-ophthalmodiagnosis (Part of: 6 Clinical examination methods)
