S cone electroretinography with a blue-light stimulus presented through a contact lens electrode

We tested a new procedure to evaluate human S cones by electroretinography ERG). The eye to be tested was fitted with a contact lens containing a blue-light-emitting diode (blue LED; NICHIA NLPB500, λmax=450 nm), and a slide projector (Kodak Carousel 5600) placed 30 cm from the subject provided diffuse yellow background illumination (Kodak Wratten 12). The amplifier used had a high-pass cutoff of 100 Hz and time constant of 0.1 second, and 64 responses were averaged. A small b-wave with a peak latency of 55 to 60 ms and an amplitude of 2.9 to 5.8 μV was recorded from normal subjects, and a similar b-wave was recorded from those with blue cone monochromacy and fundus albipunctatus. These results suggest that using a blue LED contact lens electrode is effective for eliciting ERG responses from human S cones.