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Ambreen Tariq, Ibrahim Sheriff, Taha Bhatti, Ahmed Sankoh, Hong Gao, Christopher J Hammond, Omar Abdul Rahman Mahroo; Effect of varying conductive fibre electrode position between fornix and lid margin on electroretinogram amplitudes and implicit times. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5121.
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© ARVO (1962-2015); The Authors (2016-present)
Techniques for recording the electroretinogram (ERG) include using contact lens, gold foil, and conductive fibre electrodes; different methods yield different response amplitudes. We explored the effect of varying the position of the conductive fibre electrode on responses recorded from the same subject, elicited by standard stimuli.
Full-field ERG responses were recorded from both eyes in 6 healthy subjects: in one session, electrodes were placed in the lower conjunctival fornix in both eyes; in a different session, the electrode was placed at the lid margin in one eye and left at the fornix in the other eye (which served as a control). Stimuli were delivered according to ISCEV standards, using the full set of scotopic and photopic stimuli in 3 subjects and only the photopic stimuli in 3 subjects. Pupils were pharmacologically dilated and pupil diameters were monitored throughout.
When moving from the fornix to the lid margin the mean increase in 30 Hz flicker amplitudes was 44.9% (range 5.5 to 82.7%). Mean increases in photopic a-wave and b-wave amplitudes were respectively 47.3% (range 29.4 to 68.0%) and 44.3% (range 17.2 to 86.7%). Mean increases in implicit times were between 0.4 and 2.5% for all photopic stimuli. For scotopic stimuli, the mean increase in dim-flash b-wave amplitude was 64.8% (range 18.2 to 98.9%), and the mean increase in a-wave and b-wave amplitudes elicited by the 3 cd m-2s flash were 47.3% (range 4.0 to 82.1%) and 44.0% (range 14.6 to 61.9%). For the 10 cd m-2s flash, mean increases were 49.2% (range 11.5 to 83.6%) and 44.6% (range 14.7 to 65.1%) respectively. Mean increases in implicit time ranged from 1.4% to 6.9% for scotopic stimuli. In the control eye, mean amplitudes did not vary by more than 21%, and mean implicit times did not vary by more than 5% between the two sessions.
Compared to the fornix, ERG response amplitudes were over 40% higher when the fibre electrode was placed at the lid margin. Implicit times did not appear to change more than in the control eye. This would be consistent with changes in position having a scaling effect on response amplitudes, with little effect on latencies, and shows the importance of consistent electrode positioning in recordings.
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