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Editors Selection IGR 14-3

Clinical Examination: Multifocal ERG

Comment by Vittorio Porciatti on:

51252 Macular function in eyes with open-angle glaucoma evaluated by multifocal electroretinogram, Parisi V; Ziccardi L; Centofanti M et al., Investigative Ophthalmology and Visual Science, 2012; 53: 6973-6980

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In glaucoma, retinal ganglion cells and their axons are primarily affected. There is still controversy on whether outer retinal neurons are spared. To answer this question, Parisi and collaborators recorded the multifocal ERG (mfERG) in 24 patients with treated glaucoma (Humphrey 24-2 MD ranging between -2 and -12 dB; PSD between +2 and + 10 dB) using and array of 61 hexagons spanning an area of 20 deg radius centered on the fovea. Response analysis was conducted for concentric rings of increasing eccentricities. mfERG waveforms typically consisted of a negative (N1) ‐positive (P1) waves, which are thought to originate from photoreceptor and OFF bipolar cells. Compared to mfERGs of 14 normal controls, mfERGs of patients had significantly reduced amplitude density for the macular rings (0 to2.5 deg and 2.5 to 5 deg eccenticity) but not for more peripheral rings. Parisi and collaborators suggest that in this group of patients there was a selective impairment of the macular mfERGs, which was consistent with dysfunction of the pre-ganglionic foveal cell population. They speculate that mfERG losses could be associated with decreased choroidal blood flow in the macula. The mfERG may be a valuable tool when it is combined with visual fields obtained concurrently. While in this study macular mfERG losses were significantly worse in patients with more compromised global visual field indices MD and PSD, there was no spatial correspondence between local mfERG densities and local visual field sensitivities. This is in agreement with previous reports showing that local mfERG changes in glaucoma are not correlated with local field defects.

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