Influence of Recording Electrode Type and Reference Electrode Position on the Canine Electroretinogram

Abstract

Electroretinography is commonly used to assess the functional integrity of the retina. There are many external variables that can influence the electroretinographic waveforms recorded, and it is important to be aware of these so as not to misinterpret their effects as abnormalities in retinal function. In this study we examined the effect of three different recording electrodes on the ERGs recorded from normal dogs. A bipolar Burian-Allen lens, a monopolar Dawson Trick Litzkow (DTL) fiber electrode, and a monopolar ERG-Jet lens electrode were compared. The effect of altering the distance of the reference electrode from the eye was also examined; using the ERG-Jet lens electrode, the ERG was recorded with the reference electrode placed over the zygomatic arch at 1, 3 and 5 cm caudal to the lateral canthus. The ERGs recorded with the bipolar Burian-Allen lens had significantly lower amplitudes, higher a-wave thresholds and a shallower initial a-wave slope, than those recorded by the two monopolar electrodes. Positioning the reference electrode further from the eye resulted in significantly higher amplitudes. Naka-Rushton fitting and calculation of retinal sensitivity (K) gave significantly different results between the Burian-Allen lens and ERG-Jet lens electrode with the reference electrode 5 cm from the lateral canthus. These results demonstrate that recording electrode type and distance of the reference electrode from the eye significantly affect the ERG tracings of the dog, and may alter the assessment of retinal function that can therefore be derived. Results obtained using these three different types of electrodes cannot be directly compared.

Determinação dos valores normais do eletrorretinograma de campo total em cães da raça Poodle portadores de catarata de acordo com a faixa etária

“…Assim sendo, o ERG nesses animais torna-se indispensável quando não se é capaz de ver o fundo do olho. A interpretação do ERG deve ser feita levando-se em consideração a espécie, raça e idade do animal, além da opacidade de meios, do tipo de eletrodo, do eletrorretinógrafo e do protocolo de sedação (MENTZER et al, 2006). NARFSTRÖM et al (2002) afirmam que não é possível comparar ERG de raças distintas, por apresentarem diferenças anatômicas, mesmo empregando um único protocolo anestésico.…”

“…Em virtude da presença de muitas variáveis, como método de registro, estímulo, adaptação ao escuro, protocolo de sedação ou anestesia que podem alterar os resultados do ERG, é indicado que cada laboratório tenha seus parâmetros de normalidade (MENTZER et al, 2006;NORMAN et al, 2008). Objetivou-se, com este estudo, padronizar os valores de normalidade da resposta de bastonetes, máxima resposta e resposta de cones em cães da raça Poodle portadores de catarata madura ou hipermadura, de acordo com a faixa etária, utilizando aparelho portátil BPM 200.…”

Electroretinography in dogs: a review

“…In subsequent years, many factors influencing ERG results have been investigated. For example, the impact of the electrodes used in an examination was determined (Steiss et al 1992;Bayer et al 1999;Mentzer et al 2005). The usefulness of ERG in the diagnostics of retinal diseases has been confirmed in numerous publications (see, for example, the excellent reviews by Ofri (2002) and Ekesten (2013)).…”

“…Their type, placement and conductivity exert an important impact on the measurement result (Steiss et al 1992;Bayer et al 1999;Mentzer et al 2005). Many types of active electrodes are used: from mono-or bipolar contact lens electrodes, such as the Burian-Allen, Kooijman ( Figure 5) and Jet ( Figure 6) to gold-foil electrodes and Dawson-Trick-Litzkov fibre electrodes (Burian and Allen 1954;Lawwill and Burian 1966;Arden et al 1979;Dawson et al 1979;Kooijman and Damhof 1980;Kooijman and Damhof 1981;Grounauer 1982;Hebert et al 1996;Komaromy et al 2002;Mentzer et al 2005). Reference and ground electrodes may take the form of a subdermal needle or surface cup electrodes (Komaromy et al 2002;.…”

“…Reference and ground electrodes may take the form of a subdermal needle or surface cup electrodes (Komaromy et al 2002;. Electrode placement also has an impact on the shape and magnitude of ERG traces (Mentzer et al 2005). Since the eyeball is like an electrical dipole, the positioning of electrodes near its poles results in the best response (Mentzer et al 2005;Ekesten et al 2013).…”