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This Article Full Text Full Text (PDF) All Versions of this Article: 570/2/325    most recent jphysiol.2005.098046v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lalonde, M. R. Articles by Tremblay, F. Search for Related Content PubMed PubMed Citation Articles by Lalonde, M. R. Articles by Tremblay, F. Related Collections Neuroscience

¹ Retina and Optic Nerve Research Laboratory
² Department Physiology & Biophysics
³ Department Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7

Non-invasive recordings of the retinal activity have an important role to play in the diagnosis of retinal pathologies. The detection of diseases that involve retinal ganglion cells (RGCs), such as optic atrophy and glaucoma, may be improved by isolating the RGC contribution from the multifocal electroretinogram (mfERG). In this study, mfERGs were performed on 20 pigs, 1–6 weeks following unilateral retrobulbar optic nerve section (ONS). The stimuli were 103 non-scaled high-contrast hexagons from which summed and individual mfERG responses were obtained in experimental and control fellow eyes under conditions of ketamine (n= 11) or isoflurane anaesthesia (n= 9). The effect of intravitreal injection of tetrodotoxin (TTX; n= 6) was also investigated. The summed mfERG responses showed a first positive peak (P1) with a short latency (21 ms) followed by two smaller peaks (P2 and P3) of longer latency (46 and 65 ms, respectively). While P2 and P3 amplitude were highly correlated with the time post-optic nerve section (ONS) (P2: r²= 0.669; P= 0.007; P3: r²= 0.651; P= 0.005), P1 was not (r²= 0.193; P= 0.38). P1 and P2 showed no implicit time variation as a function of retinal location, while P3 implicit time varied along the axis of the visual streak, generating a naso-temporal asymmetry. However, the P3 implicit time did not vary consistently with distance away from the optic nerve head. Intravitreal injections of TTX reduced P2 and P3 in the control eyes, consistent with the effect of ONS, and also induced a series of regular oscillations lasting up to 200 ms post stimulus. Under isoflurane anaesthesia, all components of the mfERG ifn experimental and control eyes were, at all time points post-ONS, of similar amplitude and without naso-temporal asymmetry, suggesting a reduced participation of RGCs under these anaesthesic conditions. These data clearly demonstrate that it is possible to isolate the RGC contribution from non-invasive multifocal electroretinography.

(Received 2 September 2005; accepted after revision 8 November 2005; first published online 10 November 2005)
Corresponding author F. Tremblay: IWK Health Centre, 5850/5890 University Avenue, Halifax, NS, Canada. B3K 6R8. Email: ftrembla{at}dal.ca

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