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M. C. Brown, A. C. Stopforth, R. P. Hagan, A. C. Fisher; The Effect of Electrical Interaction Between Eyes on Electro-Oculogram (EOG) Recordings. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2892.
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To determine the content of the EOG signal which is derived from the fellow eye, and to assess its impact on interpretation of results, with special reference to cases with asymmetrical responses.
The clinical EOG-test records the changes in standing electrical potentials generated by the retina in light and dark conditions. The result is usually expressed as the Arden ratio, which is the ratio of the peak potential developed in the light to the minimum (trough) occurring in darkness. In this study, previous clinical EOG recordings were examined from normal subjects and on subjects with only one working eye. From the results, an estimate of ‘cross-talk’ between the eyes has been made. In addition, results have been examined from cases where there is a significant inter-eye difference in the standing potential or the Arden Ratio, and an assessment has been made of the likely impact of the cross-talk on the results
From subjects with only one functioning eye the level of cross-talk has been found to be up to 40% with a common nasal electrode, and 15% with the standard four electrode set. With an absent fellow eye, the saccadic recordings show an inverse polarity to the functioning eye responses. In this situation the Arden Ratio can look similar for the two eyes. This phenomenon has implications when the standing potentials or the Arden Ratios are dissimilar. For instance, in the situation that the light rise is absent in one eye and the standing potential is also low, the weaker eye appears to have a ‘Negative’ EOG. If only the standing potentials are different, but with similar Arden ratios, the results are unaffected. If the standing potentials are the same, but the Arden ratios are different then the larger Arden ratio is exaggerated at the expense of the smaller one.
Arden ratios may be incorrect when there is a difference in either the standing potential or Arden Ratios derived from the two eyes due to crossover of potentials between the eyes and recording sites. If the differences are large, this may change the diagnosis. The percentage of crossover is determined mainly by the electrode positions.
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