Assessment of “non-recordable” electroretinograms by 9 Hz flicker stimulation under scotopic conditions

Abstract

To refine methods of electroretinographical (ERG) recording for the analysis of low retinal potentials under scotopic conditions in advanced retinal degenerative diseases. Standard Ganzfeld ERG equipment (Diagnosys LLC, Cambridge, UK) was used in 27 healthy volunteers (mean age 28 ± SD 8.5 years) to define the stimulation protocol. The protocol was then applied in clinical routine and 992 recordings were obtained from patients (mean age 40.6 ± 18.3 years) over a period of 5 years. A blue stimulus with a flicker frequency of 9 Hz was specified under scotopic conditions to preferentially record rod-driven responses. A range of stimulus strengths (0.0000012-6.32 scot. cd s/m² and 6-14 ms flash duration) was tested for maximal amplitudes and interference between rods and cones. Analysis of results was done by standard Fourier Transformation and assessment of signal-to-noise ratio. Optimized stimulus parameters were found to be a time-integrated luminance of 0.012 scot. cd s/m² using a blue (470 nm) flash of 10 ms duration at a repetition frequency of 9 Hz. Characteristic stimulus strength versus amplitude curves and tests with stimuli of red or green wavelength suggest a predominant rod-system response. The 9 Hz response was found statistically distinguishable from noise in 38% of patients with otherwise non-recordable rod responses according to International Society for Clinical Electrophysiology of Vision standards. Thus, we believe this protocol can be used to record ERG potentials in patients with advanced retinal diseases and in the evaluation of potential treatments for these patients. The ease of implementation in clinical routine and of statistical evaluation providing an observer-independent evaluation may further facilitate its employment.

Human flicker electroretinography using different temporal modulations at mesopic and photopic luminance levels

“…Bijveld et al [6] found that, using green flash stimuli, the transition from rod-to cone-driven ERGs occurs at 0.3 cd/m 2 . Schatz et al [27] found that the transition between the rod-and cone-dominated ERGs with blue and green flashes occurred at 0.16 scotopic cd/m 2 [27]. This value is well below our findings (approximately 10 scotopic cd/m 2 with white LED stimulation).…”

Rod and Cone Function in Patients with KCNV2 Retinopathy

“…Finally, dark-adapted responses to a series of blue flicker (LED 470 nm) with an intensity of 0.03 cd.s/m 2 and frequencies between 5 and 30 Hz were recorded to isolate temporal retinal characteristics of the rod system [24].…”

Transcorneal Electrical Stimulation for Patients With Retinitis Pigmentosa: A Prospective, Randomized, Sham-Controlled Follow-up Study Over 1 Year

“…The ERG protocol consisted of 4 steps with 4 ms duration. A single flash (3 cd.s/m 2 ; white 6500 K) response and a 9 Hz flicker (0.16 cd.s/ m 2 ; blue LED 470 nm as described previously 19 ) were used as rod protocol. A single-flash cone response and a 30 Hz flicker (both with 3 phot cd.s/m 2 stimulation intensity in presence of a background illumination of 30 phot cd/m 2 ) were chosen as cone protocol.…”