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Vaegan, P. Beaumont; The Fast Oscillation of the Electroculogram Is a Rapidly Recorded Independent Parameter, Sensitive to and Specific for Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2005;46(13):515.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Fast oscillation (FO) measurement is described but not required in the ISCEV standard electroculogram (EOG). We previously found EOG scores were independent, 4 FO cycles were enough. They replaced preadaptation without affecting test time. FOs were small in most cases of retinitis pigmentosa (RP) but seldom in 13 other classes of disease. We used tighter controls of stimulation and diagnosis, to reexamine these relationships in a much larger sample. Methods: 1029 complete EOGs were recorded with definite diagnosis in 861 cases classified into 14 major clinical groups. Pupils were dilated >8mm. Impedance was <3Kohm. Ganzfeld background was 200cd.m–2. Each FO 1 min phase commenced immediately after 15 sec of eye movements. There were 2 to 7 cycles of light (200 cd/m2) and complete dark phases preceding the EOG. The first cycle was ignored. We recorded a running average of maximum excursion amplitudes in the preceding 4sec. The maximum amplitude in all dark and light phases and dark trough and light peak times were recorded. We calculated the FO (mean dark/light) for increasing nos of cycles and the Arden ratio for each eye. All outlying data was checked for accuracy. Cases with missing scores were rejected. Principal component factor analysis was applied and normal ranges of scores plotted across major groups. Results: Correlations between and within eyes were similar. Five factors emerged. Amplitude, weighing equally on dark trough and light peak, accounted for 22% of the variance. The other factors, loading on the FO, the Arden ratio and the two times accounted for about 16% each. Amplitude correlated positively with the FO and negatively with the Arden Ratio in the orthogonal solution. Amplitudes and Arden Ratios were abnormal in many clinical groups and most frequently in RP (>85%) but times had low variance and no correlation to disease. The FO was low in >75% of RP cases and <20% in other diseases. Conclusions: The FO is an independent EOG parameter with a unique place in clinical electrodiagnosis. It is sensitive to and specific for RP and can be recorded with skin electrodes in <12 min. A combination of an abnormal FO and an abnormal standard EOG (Arden ratio and/or amplitude) is very specific to RP. The ERG, by contrast, takes longer and is only reduced proportionately more than is expected from the field loss, in around 50% of cases. An EOG, including an FO, therefore has an important place in RP diagnosis, especially for patients with early disease and especially children and who cannot accept ERG electrodes.
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