In primary pigmentary retinal degeneration (retinitis pigmentosa) the electroretinogram (ERG) has been reported to be extinguished (Karpe, 1945; Björk and Karpe, 1951; Armington, 1954; François, 1952; Dodt and Wadensten, 1954). The ERG as used by Karpe and his followers is purely a measure of rod function, and in these first investigations the highly specific depression of the ERG (especially of the b-wave) was thought to confirm the theory that the disease was a primary degeneration of the rods. However, some discrepancies soon became apparent. Dodt and Wadensten (1954) and Riggs (1954) commented that in patients with well-preserved vision no electrical response could be recorded at all, even though the light intensities and conditions of the test were such that the photopic system of the retina was active. Riggs suggested that functional "perforations" occurred in the retinal periphery, which acted as electrical shunts and prevented the remote corneal electrode picking up
ARDEN GB, FOJAS MR. Electrophysiological Abnormalities in Pigmentary Degenerations of the Retina: Assessment of Value and Basis. Arch Ophthalmol. 1962;68(3):369–389. doi:10.1001/archopht.1962.00960030373012
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