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K. Bradshaw; Post–Receptoral Components of the Human Cone–Driven ERG . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1665.
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© ARVO (1962-2015); The Authors (2016-present)
Compare ERG responses to red flash stimuli presented against a blue background and when presented just after extinguished the background.
ERGs were recorded to a red flash stimulus presented against a blue rod–saturating background of 38sc.cd.m–2. There were 3 experiments: (1) Responses were recorded in 4 normal subjects to stimuli ranging in intensity from 0.01 to 50 ph.cd.s.m–2 presented against a blue background. (2) Experiment 1 was repeated but the blue background was extinguished 200ms before the stimulus flash. (3) Responses were recorded in 3 subjects to a 0.86 and a 23.0 ph.cd.s.m–2 red flash presented 0–300ms after the blue background was switched off; the same responses were also recorded in a patient with unilateral inner retinal abnormality.
(1) A–wave amplitude increased rapidly and was maximal to stimulus intensities of about 20 ph.cd.s.m–2 but b–wave and PhNR amplitudes were maximal to much lower intensities (1–2 ph.cd.s.m–2) and amplitudes were reduced to more intense stimuli. The number of OPs increased from 2–4 over the intensity range and the i–wave was resolved only to stimuli ranging from 0.2–6 ph.cd.s.m–2. (2) A–wave amplitude increased significantly when the blue background was extinguished 200ms before the stimulus flash. Measuring the a–wave at times between 6 and 14ms showed that amplitude increase was greatest at later times and was substantial even at low stimulus intensities. The OPs were also enhanced especially at low intensities but b–wave and PhNR amplitudes were not affected by extinguishing the background. (3) At shorter stimulus delays a second slower negative phase followed the initial rapid rise in a–wave amplitude. This second phase and maximal amplitude occurred for stimulus delays in the region of 75ms. Amplitude increase was less and transient at early times of measurement (<10ms) of the a–wave but much greater and more prolonged at later times. Other components were not affected significantly by stimulus delay and results were similar at the two stimulus intensities. The patient’s ERG was dominated by early negative components and the increase of a–wave amplitude with stimulus delay was much greater than normal; the b–wave and OPs could not be identified to more intense stimuli.
All ERG components reached maximal amplitude to relatively low energy stimuli. A–wave amplitude increased if the stimulus was presented a short time after extinguishing the background light. The increase was greatest at later times of measurement of the a–wave suggesting recovery of post–receptoral cells. The amplitude of other ERG components was not affected.
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