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M. K. Menz, M. D. Menz, E. E. Sutter, A. J. Green; New Electrophysiological Approaches for Monitoring the Visual Pathway in Multiple Sclerosis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3850.
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To study and compare optic nerve function with retinal anatomy in multiple sclerosis (MS) patients using multifocal visual evoked potentials (mfVEP), the optic nerve head component (ONHC) of the multifocal electroretinogram (mfERG), and optical coherence tomography (OCT) of the retina and nerve fiber layer.
MfERG and mfVEP were recorded from 8 normal subjects and 6 patients (5 diagnosed with MS, one probable MS). Stimulation and analysis were performed with the VERIS 5 Science system. To provide better coverage of the visual field, we used an mfVEP stimulus with 120 sectors and then applied spatial averaging or grouping. In mfERG recordings the global flash paradigm was used to emphasize and evaluate signal contributions originating at the transition from membrane to saltatory nerve conduction at the beginning of fiber myelination. We compared our functional electrophysiological tests with results obtained by OCT tests. The two OCT tests measured macular and retinal nerve fiber layer (RNFL) thickness. The Smith-Kettlewell Institute Low Luminance (SKILL) card was used for an acuity test that has proven to be sensitive to alterations in vision function due to optic neuritis (ON).
One patient with probable MS but no ON history, showed significant local unilateral mfVEP delays of between 15 and 30 ms. In approximately the same area of this eye the ONHC was reduced or absent suggesting retrobulbar demyelination. OCT nerve fiber layer thickness was normal while the macular thickness in this eye and area was slightly reduced. The SKILL score also was abnormal in this eye for a person in this age group. In an MS patient without ON, the mfVEP showed significant local delays in some areas as well as significantly reduced amplitude in the right eye. The ONHC suggested areas with retrobulbar demyelination in both eyes. OCT results were normal in both eyes. The SKILL score was slightly worse in the right eye although still within normal range. In an MS patient who had an ON attack 1.5 years ago in the right eye with full recovery, we found areas of significantly delayed mfVEP responses in this eye. MfERG and OCT results were in the normal range. The SKILL score was abnormal in both eyes.
While both mfERG and mfVEP data present substantial evidence of demyelination, the OCT results showed no conclusive evidence of fiber loss. Inter-ocular comparison of mfVEP records appears to be the most sensitive test in the presence of unilateral or asymmetric disease. The ONHC may be particularly important in patients who have relatively symmetrical ON injury.
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