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J.Y. Chen, J.G. Odel, M.M. Behrens, D.C. Hood; Unusual Effects of Retinal Abnormalities on the Multifocal Visual Evoked Potential . Invest. Ophthalmol. Vis. Sci. 2006;47(13):779.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the multifocal visual evoked potentials (mfVEP) in patients with abnormal multifocal ERGs (mfERG).
Static automated perimetry (SAP), mfERGs and mfVEPs were obtained from 17 individuals seen by two neuro–ophthalmologists and diagnosed with retinal pathology based upon funduscopic examination, visual field, and multifocal ERG. Optic neuropathy was ruled out in all cases. Diagnoses included autoimmune (4), BRAO (3), cone dystrophy (2), cone rod dystrophy (1), BRVO (1), vitamin A deficiency (1), MEWDS (1), and nonspecific retinal disease (4). Patients were selected from a larger group based upon abnormal mfERG amplitudes in greater than 30% of the 46 degree wide field. The mfVEPs were recorded to a pattern reversing 60 sector display and compared to mfVEPs from 50 age matched controls1. Estimates of SAP loss in the same regions of the field used for the mfVEP and mfERG were obtained by interpolating the SAP values.
14 of 17 (82%) patients showed significant delays on their mfVEP, as determined by either mean latency or the probability of a cluster of delayed local responses2. The mfVEPs were significantly more delayed than mfVEPs from patients with glaucoma (p<0.0001) or ischemic optic neuropathy (p<0.001), but not when compared to patients with optic neuritis (p=0.15)3. For all 17 patients, the mfVEP showed local responses where amplitudes were abnormal. However, in 14 of 17 patients there were normal mfVEP amplitudes in areas of profoundly decreased SAP sensitivity. In addition, in 15 of 17 patients, there were measurable mfVEP amplitudes in regions with little to no mfERG response. These findings can be mimicked in normal individuals by viewing the display through a neutral density filter.
Some retinal abnormalities can produce significantly delayed mfVEP responses leaving amplitudes relatively large in regions of depressed SAP sensitivity and mfERG amplitude. The neutral density results suggest that the effects of these retinal abnormalities are occurring, in part, before major gain changes. Not all retinal abnormalities behave in this fashion, as conditions such as retinitis pigmentosa, which destroy large regions of receptors, can present with undetectable local mfVEPs. Clinicians who use the mfVEP for purposes of diagnosing optic nerve disease should take care not to confuse delays due to a retinal disease with delays due to demyelinating diseases. 1. Fortune et al. (2004) DOOP. 2. Hood et al. (2004) DOOP. 3. Odel et al. (2005) ARVO.
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