For anyone having similar troubles with the ERG procedure, I recommend the following materials:

Article Ex vivo electroretinograms made easy: performing ERGs using ...

https://ideaexchange.uakron.edu/cgi/viewcontent.cgi?article=3130&context=honors_research_projects

Article Simultaneous ex vivo Functional Testing of Two Retinas by in...

With the help of Dr. Mark Emerson at the CCNY (http://emersonlabccny.com/), I was able to dissect A. burtoni eye to isolate the retina. The A. burtoni retina is particularly challenging to isolate from the retinal pigment epithelium (RPE) because great care must be taken when peeling away the layer. If mishandled, the RPE can crumble into what looks like grainy particles that are extremely difficult to remove without damaging the underlying retina.

I am still researching whether it is more appropriate to leave the RPE attached to the retina or remove it. On one hand, the RPE increases the signal-to-noise ratio, complicating subsequent analysis. On the other hand, removing the RPE eliminates the retina's recycling station, which impairs cone function.

Additionally, pharmacological agents may be required to isolate specific contributions to the a- and b-waves (as discussed in the papers above), making a fully isolated retina more suitable in such cases.

Overall, I am leaning toward fully isolated retina and hope that conducting an ERG within an hour of retina removal, combined with an appropriate perfusion system, will generate high-quality a- and b-wave data.

This is just a progress update. If anyone has suggestions, please share! Thank you again.