Raj K. This test helps us discriminate between optic-nerve and retinal disease, detect early hydroxychloroquine toxicity, diagnose and distinguish between the various white dot syndromes and follow patients with inherited retinal diseases who have extinguished Ganzfeld ERGs. We describe the principles behind this new technology and present clinical examples so that the reader can better understand when to refer a patient for this specialized testing. TBD Figure 1. The typical mfERG setup includes a contact lens electrode on the cornea connected to an electrically isolated amplifier. The patient views a monitor displaying a rapidly changing sequence of hexagons.
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Corresponding author. Corresponding author: Laura J. Davis Armistead Bldg. Abstract Purpose. To determine retinal pathway origins of pattern electroretinogram PERG in macaque monkeys using pharmacologic dissections, uniform-field flashes, and PERG simulations.
PERGs were also recorded from macaques with advanced unilateral experimental glaucoma, and were simulated by averaging ON and OFF responses to uniform-field flashes.
For 8. Blockade of all postreceptoral activity eliminated transient and steady state PERGs, but left small residual P1 in simulations. N95 reflects spiking activity of ganglion cells; P50 reflects nonspiking activity as well. The pattern electroretinogram PERG is commonly recorded noninvasively from the cornea under light-adapted conditions using a checkerboard or grating pattern with equal numbers of bright and dark elements.
The lower frequencies e. It is assumed that since the overall luminance of the pattern stimulus remains constant, the linear responses for all frequencies of stimulation that contribute to standard waves e. However, nonspiking portions of P50 may, in some pathologic situations, reflect activity of more distal neurons.
Indications with respect to these issues from other studies have not been entirely consistent. The predominance of a particular pathway in formation of PERG waveforms is somewhat surprising. Viswanathan et al. The results should provide useful information for interpretation of the PERG in human patients, with pathologies that affect pathway elements distal to the ganglion cells, as well as the ganglion cells themselves.
Some of the findings were reported previously in abstract form Luo X, et al. Methods Subjects Ten adult monkeys Macaca mulatta; 7 to 10 years of age were studied. Pupils were fully dilated to approximately 8. Body temperature was maintained between Heart rate and blood oxygen were monitored with a pulse oximeter model V; Nonin Medical, Inc. Acute blockade of retinal pathways was achieved by intravitreal injection of l-AP4 hitherforth, called APB in this paper 2-aminophosphonobutyric acid, 1.
Retinal Pathway Origins of the Pattern Electroretinogram (PERG)
The electrical response is a result of a retinal potential generated by light-induced changes in the flux of transretinal ions, primarily sodium and potassium. Most often, ERGs are obtained using electrodes embedded in a corneal contact lens, which measure a summation of retinal electrical activity at the corneal surface. The ERG can provide important diagnostic information on a variety of retinal disorders including, but not limited to congenital stationary night blindness, Leber congenital amaurosis, and cancer-associated retinopathy. Moreover, an ERG can also be used to monitor disease progression or evaluating for retinal toxicity with various drugs or from a retained intraocular foreign body. James Dewar of Scotland subsequently performed it in humans in , however widespread clinical application did not occur until , when American psychologist Lorin Riggs introduced the contact-lens electrode.