Evaluation of different recording parameters to establish a standard for flash electroretinography in rodents

Different electrodes and stimulus protocols commonly used for electroretinography in rodent eyes were compared for convenience of use, degree of damage to corneal epithelium, and for magnitude of amplitude, reproducibility, left versus right eye accuracy, and reliability of recorded parameters of the flash electroretinogram (ERG). Adult C57BL/6 pigmented mice and albino Wistar rats were used to determine scotopic ERGs in response to Ganzfeld or strobe-light stimulation and light-adapted (photopic) ERGs recorded from both eyes at the same time. Test-retest data were used for statistical analyses to compare a monopolar gold-wire contact lens electrode (CLE), a cotton-wick silver-silver chloride electrode (CSCE), a DTL fiber electrode (DTLE), and a circular stainless steel wire electrode (SSE). Corneas were evaluated for abrasion after ERG recordings using fluorescein staining and also for the time taken, ease of insertion, and re-insertions required for the different electrodes. Compared to CSCE, DTLE, and SSE, the ERG potentials recorded by CLE had significantly larger scotopic amplitudes and oscillatory potentials under strobe or Ganzfeld stimulation and for light-adapted ERG b-wave amplitudes in both mice and rats. In analyzing test-retest data of scotopic ERG a-wave and b-wave amplitudes, the intraclass correlation coefficient showed the best agreement for the CLE (range 0.61-0.94) compared to the SSE (0.13-0.77), DTLE (0.02-0.69), and CSCE (0.12-0.51). In mice and rats, logistic regression analyses revealed significant correlations for amplitudes of most scotopic ERG parameters between contralateral eyes obtained with CLE and for some ERG components recorded by SSE. When comparing ERG amplitudes for stimulation by strobe or Ganzfeld, the difference was least with the CLE compared to DTLE, CSCE, or SSE. The time taken to insert the four different electrodes was greatest for the CLE in both mice and rats. The extent of corneal abrasion resulting from electrode use in mice was largest for the SSE followed by the CLE. However, in rats there was almost no corneal damage after ERG recordings with the CLE. Because of the stability of eye contact, the CLE allows ERGs to be determined over a longer recording session. Recording of scotopic and photopic (light-adapted) ERGs in rodents with monopolar gold-wire contact lens electrodes provides greater amplitudes and higher reproducibility when compared to other commonly used corneal electrodes. These electrodes are significantly better overall than others that were evaluated and should be considered for a standard protocol to monitor retinal function in rodent eyes.