S-cone ERGs elicited by a simple technique in normals and in tritanopes

Purpose: to measure changes in the relative spectral sensitivities of the d ark adapted and light adapted ERG and thus to establish the possible contri bution of rods to the 'blue cone' ERG elicited by flashes of blue light. Ba ckground: short wavelength stimuli in the light-adapted eye evoke small rou nded b-waves which have been considered to be S-cone responses. We have rec orded such responses from tritanopes, which called the assumptions into que stion. Methods: small ERGs were recorded to blue and green flashes. The sti mulus was a Ganzfeld which employed light emitting diodes. ERGs were obtain ed in both the dark-adapted eye and after light adaptation to intense orang e light (peak wavelength 610 nm). The change in sensitivity with light adap tation and the relative spectral sensitivity was determined from the voltag e/log light intensity functions, using a 10 mu V criterion. Results: (1) pe ak times and changes in sensitivity did not help distinguish light-adapted rod from possible S-cone responses; (2) analysis of the change in the ratio of blue:green sensitivity from darkness to 4.4 log Td. 610 nm background s uggests that in seven normal subjects, 90% or more of the ERG evoked by 440 nm flashes is generated by S-cones; (3) three tritanopes have insignifican tly reduced S-cone responses. Conclusions: (1) clinical techniques used to isolate S-cone ERGs are appropriate; (2) there are at least two types of tr itanope and in those we investigated, functional S-cones are probably displ aced into the retinal periphery. (C) 1998 Elsevier Science Ltd. All rights reserved.