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Brad Fortune; Local functional losses upstream from focal intraretinal laser axotomy in macaque retina. Journal of Vision 2002;2(10):112. doi: 10.1167/2.10.112.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Prior studies have shown that multifocal electroretinogram (mfERG) responses from normal monkey eyes contain signals that are likely generated by ganglion cells. Such evidence was derived from experimental conditions that have widespread effects throughout the retina and/or optic nerve, such as intravitreal injections of pharmacologic agents, optic nerve transection, or experimental glaucoma. Pathologic events and visual field loss, however, are often localized, as in human glaucoma. It remains unknown whether focal lesions (ganglion cell loss in relative isolation from global optic nerve effects) can be detected using the mfERG. The purpose of this experiment was to assess the effects of a focal retinal nerve fiber bundle axotomy on mfERG responses.
Methods: mfERGs were obtained at baseline and on several occasions after focal laser treatments induced a ‘bundle defect’ within the supero-temporal nerve fiber layer (NFL) of the left eye in one macaque monkey. Three mfERG stimulus protocols were compared: a standard fast m-sequence flicker, a “global-field flash” paradigm (Sutter et al, 1999), and a slowed m-sequence (8 video frames per m-step).
Results: The NFL bundle defect was plainly visible both proximal and distal to the site of the photoabl ation. A focal notch corresponding with the NFL defect was present within the neuro-retinal rim of the optic disk. Histologic evaluation of ganglion cell soma counts distal to the lesion is pending. mfERGs showed selective loss of high-frequency components for responses located within the arcuate region corresponding to the NFL defect. The lower-frequency components (photoreceptor and bipolar cell mediated) were well preserved. Losses were most easily detected using the slowed m-sequence stimulus.
Conclusions: Focal loss of ganglion cell function in the macaque retina can be detected using the mfERG. This evidence also supports prior full-field ERG studies that have suggested classical oscillatory potentials are reduced in human glaucoma.
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