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E.E. Sutter, A. Berezovsky, S.R. Salomao, J.M. Pereira, P.Y. Sacai, A.A. Sadun; Focal Variability of the Optic Nerve Head Component of Multifocal ERG Responses in Unaffected Carriers of 11778 LHON Suggests Retrobulbar Myelin Remodeling . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4838.
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© ARVO (1962-2015); The Authors (2016-present)
At ARVO 2004 we reported massive regional loss in the Optic Nerve Head Component (ONHC) of the multifocal ERG in unaffected carriers of the 11778 LHON mutation. These abnormalities were attributed to retrobulbar demyelination of optic nerve fibers. In two follow–up studies (2004 and 2005) our objective was to determine whether observed ONHC losses 1. Can be reproduced 2. Vary over time, 3. Lead to local delays in corresponding areas of the mfVEP. 4. Correspond to visual field loss.
Multifocal electroretinograms (mfERG) were recorded from carriers of the 11778 LHON mutation using a special stimulation mode (global flash protocol) that amplifies the optic nerve head component (ONHC). The ONHC is a signal contribution from ganglion cell axons near the optic nerve head at the point where myelination begins. 26 unaffected carriers of the 11778 mutation and 2 affected patients were tested on in November of 2004 and again in October of 2005. The morphology of the waveform was visually evaluated for abnormal features, specifically for the presence of the ONHC. The evaluation was conducted independently by two groups of investigators. Absence of the ONHC indicates either loss of axonal transmission or retrobulbar demyelination. All data were collected while monitoring the position of the stimulus on the retina with an IR fundus camera.
Out of 26 carriers 14 were rated within normal range on both occasions. 6 were rated worse in 2005 while 4 showed substantial improvements. One of these was the mother of a male carrier who converted in 2003. Areas of reduced or absent ONHC did not correspond to areas of substantial visual field loss or areas of reduced mfVEP response amplitude. MfVEP delays are small compared to those seen in multiple sclerosis, but consistent with limited retrobulbar demyelination.
The fact that glaucoma patients with a similar degree of ONHC loss have substantial visual field loss suggests that in the unaffected carriers with abnormal ONHC topographies we are dealing mainly with retrobulbar demyelination rather than fiber loss. We propose that these observed signs of demyelination and remyelination indicate risk for future conversion. Long–term follow–up is needed to test this hypothesis.
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