Improving the diagnostic potential of the photopic electroretinogram (ERG) with refined mathematical tools

Abstract

Abstract Purpose Examine if the use of refined mathematical tools increases the understanding and diagnostic potential of the photopic ERGs. Methods Analyses were performed on normal and pathological photopic ERGs (background of 30 cd.m‐2; flash intensities ranging from ‐0.8 to 2.84 log cd.sec.m‐2 in 15 steps; n>100). Mathematical instruments included: 1‐ the Continuous Wavelet Transform (CWT)2‐ The Reiman Integrator and 3‐ the Photopic Hill Gaussian:Logistic ratio [GL=Gb/(Gb+Vbmax)]claimed to weight the contribution of the OFF and ON pathways to the photopic ERG. Results 1‐ CWT revealed 3 distinct frequency domains within the 10‐50 msec poststimulus time interval, namely: 20‐40 Hz, 90‐150 Hz and 200‐300 Hz that appeared to be independently modulated by flash intensity and/or pathology. 2‐ Integration of the OPs accurately reconstructed the broadband ERGs (r>0.90), irrespective of CWT. 3‐ In our cohort of RP patients (n=50), the GL ratio was 0.43 ±0.23, compared to 0.60±0.08 in normal (p<.05). Conclusion 1‐CWT dissects the ERG into its primary components, a method that should allow a more accurate quantification of ERG responses. 2‐ Strong evidence supports the concept that the b‐wave results from the integration of the OPs. The value of the integration constant (1 sec) is close to the time constant of the Muller cell membrane suggesting that the latter could be at the origin of this integration. 3‐The broader GL distribution obtained from our RP cohort suggests that in some the OFF retinal pathway is primarily affected while in others the ON is. It remains to be determined if the latter represents two stages of the same disease process or two different disease paths. Supported by CIHR and Réseau Vision.