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M.F. Marmor, L. Cabael, M. Marcus; Comparison in Clinical Practice of ERG A–wave Parameters after Standard and High–intensity Stimuli . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5148.
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Purpose: The standard ERG a–wave represents contributions from both photoreceptor and inner retinal cells, while the leading edge of the high–intensity a–wave is produced only by photoreceptors. This has raised questions about the value of the standard a–wave as an indicator of photoreceptor disease, and has led to suggestions for standardizing higher–intensity stimuli. Our objective was to compare the behavior of standard and high–intensity a–waves in clinical practice. Methods: Standard ISCEV a–waves and high–intensity a–wave responses were recorded under scotopic and photopic conditions from normal subjects and from patients with photoreceptor dystrophies and other diseases. Results: The amplitude of standard a–waves followed closely that of the high–intensity a–wave as it varied among patients with different diagnoses. The results did not change significantly when cone a–waves were subtracted to isolate rod signals. The only exception was one patient with the enhanced S cone syndrome (ESCS) whose dark–adapted responses were cone–driven. Initial peak times clustered in a limited range for both standard and high–intensity responses, and were not very sensitive to disease. Conclusions: High–intensity a–waves show photoreceptor characteristics directly, and may help to detect some rare disorders like the ESCS. However, the amplitude of the conventional a–wave mirrors that of the high–intensity response very closely over a wide range of patients. This suggests that for practical purposes the standard a–wave is an excellent indicator of photoreceptor disease.
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