Anna Brouwer

14 Chapter 1 Electroretinogram The electroretinogram (ERG) is an objective test which assess the function of the retina. It measures the electrical signal of the cells of the retina in a response to light. In ophthalmology the ERGwas originally used to help diagnose rare retinal disorders that affect retinal function. However, it is also sometimes used to monitor the progression of disease and to assess the effect of treatment. Types of electroretinograms Over the years several types of ERGs have been developed: the full-field ERG (ffERG) also known as Ganzfield ERG, the pattern ERG (PERG), and the multifocal ERG (mfERG). 38–40 The full-field ERG measures the response of nearly the entire retina in reaction to a flash of light. This flash of light is emitted from a so-called Ganzfield dome, which ensures an even illumination of the retina. Another type of ERG, the PERG, is said to reflect the macular and ganglion cell function. 40 The mfERG is used to measure the function of different regions of the A C B RNFL GCL Axons of Ganglion Cells Nuclei of Ganglion Cells Synapses of Ganglion Cells and Bipolar Cells Nuclei of Bipolar Cells Synapses of Bipolar Cells and Photoreceptors ONL OPL ONL IS/OS junction OSL OPR RPE INL Nuclei of Photoreceptors Junction between Inner and Outer Segments of Photoreceptors Outer segments of Photoreceptors Retinal Pigment Epithelium Outer segments of Photoreceptors / Retinal Pigment Epithelium complex Figure 2: Optical coherence tomography scan of the retina in relation to retinal anatomy. A) OCT scan of the macula with segmentation lines indicating the boarders of several retinal layers. B) An enhancement of a part of OCT scan A. On the right of this enhancement is a scematic explanation of the different retinal cells of the segmented retinal layers. C) Histology biopt of a (different!) retina. Abbreviations: RNFL = Retinal Nerve Fibre Layer, GCL = ganglion cell layer, IPL = inner plexiform layer, INL = inner nuclear layer, OPL = outer plexiform layer, ONL = outer plexiform layer, IS/OS junction = inner segment outer segment junction, OLS = outer segment layer, OPR = outer segment photoreceptors/ retinal pigment epithelium complex, RPE = retinal pigment epithelium.